diff --git a/php/src/GildedRose.php b/php/src/GildedRose.php
index 608ede3b..ef44ade3 100644
--- a/php/src/GildedRose.php
+++ b/php/src/GildedRose.php
@@ -29,6 +29,12 @@ final class GildedRose
         ・計算後sell_inが0以上の場合、quality+1する
         [商品：Sulfuras]
         ・sell_in、qualityどちらも変更しない
+        [商品：Backstage passes]
+        ・引数のsell_inを-1する
+        ・引数のqualityを+1する
+            ・計算後sell_inが10未満の場合、さらにquality+1する
+            ・計算後sell_inが5未満の場合、さらにquality+1する
+            ・計算後sell_inが0未満の場合、qualityを0にする
     */
 
     /**
@@ -43,6 +49,9 @@ final class GildedRose
             } elseif ($this->item->name === 'Sulfuras, Hand of Ragnaros') {
                 // 商品：Sulfurasの処理
                 $this->sulfuras();
+            } elseif ($this->item->name === 'Backstage passes to a TAFKAL80ETC concert') {
+                // 商品：Backstage passesの処理
+                $this->backstagePasses();
             }
         }
     }
@@ -69,6 +78,28 @@ final class GildedRose
         // 何もしない
     }
 
+    /**
+     * 商品：Backstage passes計算処理
+     */
+    private function backstagePasses(): void
+    {
+        $this->calcSellInSubtraction();
+        $this->calcQualityAddition();
+
+        // sell_inが10未満の場合、qualityを再加算する
+        if ($this->item->sell_in < 10) {
+            $this->calcQualityAddition();
+        }
+        // sell_inが5未満の場合、qualityを再加算する
+        if ($this->item->sell_in < 5) {
+            $this->calcQualityAddition();
+        }
+        // sell_inが0未満の場合、qualityを0する
+        if ($this->item->sell_in < 0) {
+            $this->item->quality = 0;
+        }
+    }
+
     /**
      * sell_inの減算を行う
      */
diff --git a/php/tests/GildedRoseTest.php b/php/tests/GildedRoseTest.php
index 0be1cbc3..0b6408b5 100644
--- a/php/tests/GildedRoseTest.php
+++ b/php/tests/GildedRoseTest.php
@@ -81,6 +81,118 @@ class GildedRoseTest extends TestCase
         $this->assertSame(80, $items[0]->quality);
     }
 
+    /**
+     * Backstage passes：sell_inが11以上、qualityが50未満
+     * 期待値：sell_inが-1、qualityが+1
+     */
+    public function testBackstagePassesNormal(): void
+    {
+        $items = [new Item('Backstage passes to a TAFKAL80ETC concert', 20, 20)];
+        $gildedRose = new GildedRose($items);
+        $gildedRose->updateQuality();
+        $this->assertSame('Backstage passes to a TAFKAL80ETC concert', $items[0]->name);
+        $this->assertSame(19, $items[0]->sell_in);
+        $this->assertSame(21, $items[0]->quality);
+
+        $items = [new Item('Backstage passes to a TAFKAL80ETC concert', 11, 49)];
+        $gildedRose = new GildedRose($items);
+        $gildedRose->updateQuality();
+        $this->assertSame('Backstage passes to a TAFKAL80ETC concert', $items[0]->name);
+        $this->assertSame(10, $items[0]->sell_in);
+        $this->assertSame(50, $items[0]->quality);
+    }
+
+    /**
+     * Backstage passes：sell_inが6〜10、qualityが50未満
+     * 期待値：sell_inが-1、qualityが+2
+     */
+    public function testBackstagePassesSellIn6OrMoreAndSellIn10OrLess(): void
+    {
+        $items = [new Item('Backstage passes to a TAFKAL80ETC concert', 6, 20)];
+        $gildedRose = new GildedRose($items);
+        $gildedRose->updateQuality();
+        $this->assertSame('Backstage passes to a TAFKAL80ETC concert', $items[0]->name);
+        $this->assertSame(5, $items[0]->sell_in);
+        $this->assertSame(22, $items[0]->quality);
+
+        $items = [new Item('Backstage passes to a TAFKAL80ETC concert', 10, 20)];
+        $gildedRose = new GildedRose($items);
+        $gildedRose->updateQuality();
+        $this->assertSame('Backstage passes to a TAFKAL80ETC concert', $items[0]->name);
+        $this->assertSame(9, $items[0]->sell_in);
+        $this->assertSame(22, $items[0]->quality);
+    }
+
+    /**
+     * Backstage passes：sell_inが1〜5、qualityが50未満
+     * 期待値：sell_inが-1、qualityが+3
+     */
+    public function testBackstagePassesSellIn1OrMoreAndSellIn5OrLess(): void
+    {
+        $items = [new Item('Backstage passes to a TAFKAL80ETC concert', 1, 20)];
+        $gildedRose = new GildedRose($items);
+        $gildedRose->updateQuality();
+        $this->assertSame('Backstage passes to a TAFKAL80ETC concert', $items[0]->name);
+        $this->assertSame(0, $items[0]->sell_in);
+        $this->assertSame(23, $items[0]->quality);
+
+        $items = [new Item('Backstage passes to a TAFKAL80ETC concert', 5, 20)];
+        $gildedRose = new GildedRose($items);
+        $gildedRose->updateQuality();
+        $this->assertSame('Backstage passes to a TAFKAL80ETC concert', $items[0]->name);
+        $this->assertSame(4, $items[0]->sell_in);
+        $this->assertSame(23, $items[0]->quality);
+    }
+
+    /**
+     * Backstage passes：sell_inが0以下、qualityが50未満
+     * 期待値：sell_inが-1、qualityが+1
+     */
+    public function testBackstagePassesSellIn0OrLess(): void
+    {
+        $items = [new Item('Backstage passes to a TAFKAL80ETC concert', 0, 20)];
+        $gildedRose = new GildedRose($items);
+        $gildedRose->updateQuality();
+        $this->assertSame('Backstage passes to a TAFKAL80ETC concert', $items[0]->name);
+        $this->assertSame(-1, $items[0]->sell_in);
+        $this->assertSame(0, $items[0]->quality);
+
+        $items = [new Item('Backstage passes to a TAFKAL80ETC concert', -1, 20)];
+        $gildedRose = new GildedRose($items);
+        $gildedRose->updateQuality();
+        $this->assertSame('Backstage passes to a TAFKAL80ETC concert', $items[0]->name);
+        $this->assertSame(-2, $items[0]->sell_in);
+        $this->assertSame(0, $items[0]->quality);
+    }
+
+    /**
+     * Backstage passes：qualityが50
+     * 期待値：sell_inが-1、qualityは変更なし
+     */
+    public function testBackstagePassesQuality50(): void
+    {
+        $items = [new Item('Backstage passes to a TAFKAL80ETC concert', 11, 50)];
+        $gildedRose = new GildedRose($items);
+        $gildedRose->updateQuality();
+        $this->assertSame('Backstage passes to a TAFKAL80ETC concert', $items[0]->name);
+        $this->assertSame(10, $items[0]->sell_in);
+        $this->assertSame(50, $items[0]->quality);
+
+        $items = [new Item('Backstage passes to a TAFKAL80ETC concert', 6, 50)];
+        $gildedRose = new GildedRose($items);
+        $gildedRose->updateQuality();
+        $this->assertSame('Backstage passes to a TAFKAL80ETC concert', $items[0]->name);
+        $this->assertSame(5, $items[0]->sell_in);
+        $this->assertSame(50, $items[0]->quality);
+
+        $items = [new Item('Backstage passes to a TAFKAL80ETC concert', 1, 50)];
+        $gildedRose = new GildedRose($items);
+        $gildedRose->updateQuality();
+        $this->assertSame('Backstage passes to a TAFKAL80ETC concert', $items[0]->name);
+        $this->assertSame(0, $items[0]->sell_in);
+        $this->assertSame(50, $items[0]->quality);
+    }
+
     /**
      * 複数商品
      */
@@ -89,6 +201,7 @@ class GildedRoseTest extends TestCase
         $items = [
             new Item('Aged Brie', 5, 10),
             new Item('Sulfuras, Hand of Ragnaros', 5, 80),
+            new Item('Backstage passes to a TAFKAL80ETC concert', 5, 10),
         ];
         $gildedRose = new GildedRose($items);
         $gildedRose->updateQuality();
@@ -98,6 +211,9 @@ class GildedRoseTest extends TestCase
         $this->assertSame('Sulfuras, Hand of Ragnaros', $items[1]->name);
         $this->assertSame(5, $items[1]->sell_in);
         $this->assertSame(80, $items[1]->quality);
+        $this->assertSame('Backstage passes to a TAFKAL80ETC concert', $items[2]->name);
+        $this->assertSame(4, $items[2]->sell_in);
+        $this->assertSame(13, $items[2]->quality);
     }
 
     // テストエラーの原因が特定できないので後で調査する