The Stone Treasure Hall, which appears as a large stone in the Harima Province Fudoki (ancient provincial gazetteer), is a megalithic artifact whose purpose remains unknown. The deities enshrined at Iwaishi Shrine are Ōanamuchi-no-Mikoto and Sukunahikona-no-Mikoto. They are enshrined in the split worship hall behind the shrine office.

The two deities, sent from Izumo Province to pacify Harima Province, attempted to build a stone palace, but it remained unfinished due to a rebellion by the local gods. The spirits of the two deities resided in this stone, declaring, "We will pacify the land forever," and since then, it has been revered as "Ishi no Hōden" (Stone Treasure Hall) and "Shizu no Iwaya" (Pacifying Rock Chamber).

The megalith, also known as the Floating Stone, is so named because water collects beneath it, making it appear as if it is floating.

The Stone Treasure Hall measures 6.4 meters wide, 5.7 meters high, and 7.2 meters deep, weighing approximately 500 tons.

播磨国風土記にも大石として登場する石の宝殿は、目的が不明なままの巨石遺物です。生石神社の御祭神は、大穴牟遅命と少毘古那命の二神。社務所の奥、割拝殿に奉られています。
出雲国より播磨国を鎮めるため使わされた二神は、石造りの宮殿を建てようとしたものの土着神の反乱により未完成に終る。二神の霊はこの石に宿り「永劫に国土を鎮めん」と言明、以来「石宝殿（いしのほうでん）」「鎮の岩室（しずのいわや）」として信仰を集めてきました。
浮き石とも呼ばれるご神体の巨石の下は、水が溜まっており、水に浮いているように見える事からそう呼ばれています。
石の宝殿の大きさは、横6.4メートル、高さ5.7メートル、奥行7.2メートル、重さ約500トンにもなります。