diff --git a/php/src/GildedRose.php b/php/src/GildedRose.php
index 5751a93e..6e1b1239 100644
--- a/php/src/GildedRose.php
+++ b/php/src/GildedRose.php
@@ -38,10 +38,11 @@ final class GildedRose
         [商品：Conjured]
         ・引数のsell_inを-1する
         ・引数のqualityを-2する
+            ・sell_inが0未満の場合、さらにquality-2する
         [その他商品]
         ・引数のsell_inを-1する
         ・引数のqualityを-1する
-            ・sell_inが0未満の場合、さらにquality-1する ★仕様書に記載なかったがコード上はこのようになっている
+            ・sell_inが0未満の場合、さらにquality-1する
     */
 
     /**
@@ -119,9 +120,12 @@ final class GildedRose
     private function conjured(): void
     {
         $this->calcSellInSubtraction();
-        // 新たな関数は作成せず減算処理を2回実行する
-        $this->calcQualitySubtraction();
-        $this->calcQualitySubtraction();
+        $this->calcQualityDoubleSubtraction();
+        
+        // sell_inが0未満の場合、sell_inを再減算する
+        if ($this->item->sell_in < 0) {
+            $this->calcQualityDoubleSubtraction();
+        }
     }
 
     /**
@@ -167,4 +171,20 @@ final class GildedRose
             --$this->item->quality;
         }
     }
+
+    /**
+     * qualityを2倍の減算を行う
+     */
+    private function calcQualityDoubleSubtraction(): void
+    {
+        // 1以上の場合計算
+        if ($this->item->quality >= 1) {
+            $this->item->quality -=2;
+        }
+
+        // qualityが0未満の場合、0を設定
+        if ($this->item->quality < 0) {
+            $this->item->quality = 0;
+        }
+    }
 }
diff --git a/php/tests/GildedRoseTest.php b/php/tests/GildedRoseTest.php
index 7ffe28be..e316fd8d 100644
--- a/php/tests/GildedRoseTest.php
+++ b/php/tests/GildedRoseTest.php
@@ -284,6 +284,62 @@ class GildedRoseTest extends TestCase
         $this->assertSame(0, $items[0]->quality);
     }
 
+    /**
+     * Conjured：sell_inが0以下、qualityが50未満
+     * 期待値：sell_inが-1、qualityが-4
+     */
+    public function testConjuredSellIn0OrLess(): void
+    {
+        $items = [new Item('Conjured Mana Cake', 0, 10)];
+        $gildedRose = new GildedRose($items);
+        $gildedRose->updateQuality();
+        $this->assertSame('Conjured Mana Cake', $items[0]->name);
+        $this->assertSame(-1, $items[0]->sell_in);
+        $this->assertSame(6, $items[0]->quality);
+
+        $items = [new Item('Conjured Mana Cake', -1, 10)];
+        $gildedRose = new GildedRose($items);
+        $gildedRose->updateQuality();
+        $this->assertSame('Conjured Mana Cake', $items[0]->name);
+        $this->assertSame(-2, $items[0]->sell_in);
+        $this->assertSame(6, $items[0]->quality);
+    }
+
+    /**
+     * Conjured：sell_inが0以下、qualityが2以下
+     * 期待値：sell_inが-1、qualityを減算、0が下限
+     */
+    public function testConjuredSellIn0OrLessAndQuality2OrLess(): void
+    {
+        $items = [new Item('Conjured Mana Cake', 0, 2)];
+        $gildedRose = new GildedRose($items);
+        $gildedRose->updateQuality();
+        $this->assertSame('Conjured Mana Cake', $items[0]->name);
+        $this->assertSame(-1, $items[0]->sell_in);
+        $this->assertSame(0, $items[0]->quality);
+
+        $items = [new Item('Conjured Mana Cake', 0, 1)];
+        $gildedRose = new GildedRose($items);
+        $gildedRose->updateQuality();
+        $this->assertSame('Conjured Mana Cake', $items[0]->name);
+        $this->assertSame(-1, $items[0]->sell_in);
+        $this->assertSame(0, $items[0]->quality);
+    }
+
+    /**
+     * Conjured：sell_inが0、qualityが0
+     * 期待値：sell_inが-1、qualityは変更なし
+     */
+    public function testConjuredSellIn0AndQuality0(): void
+    {
+        $items = [new Item('Conjured Mana Cake', 0, 0)];
+        $gildedRose = new GildedRose($items);
+        $gildedRose->updateQuality();
+        $this->assertSame('Conjured Mana Cake', $items[0]->name);
+        $this->assertSame(-1, $items[0]->sell_in);
+        $this->assertSame(0, $items[0]->quality);
+    }
+
     /**
      * 複数商品
      */