According to the temple's tradition, the main deity of Daieiji Temple, Fudo Myoo, is said to be a creation of the great Buddhist monk Kobo Daishi. It's believed that during his ascent to Kyoto, Taira no Masakado brought this Fudo Myoo statue from To-ji Temple and enshrined it as the main deity in Kanto. Presently, this main deity, the Mountain and River Fudo Myoo (a wooden seated Fudo Myoo statue), is preserved in the storage behind the main hall. Daiei-ji Temple, known as "Yamakawa no Ofudo-san," is cherished by people in the neighboring towns and cities. On the 28th of every month, a special day for the deity, many stalls line up from the mountain gate to the main hall.
寺伝によれば、大栄寺の本尊である不動尊は弘法大師の作といわれ、平将門（たいら の まさかど）が京都へ上ったときに、東寺に安置されていたものを守り本尊として関東に持ち帰ったと記されています。現在、この本尊山川不動尊（木造不動明王坐像）は、本堂裏の収蔵庫に安置保管されています。大栄寺は、「山川のお不動さん」として、近隣市町村の人々から親しまれ、毎月28日の縁日は、山門から本堂までたくさんの露店が立ち並びます。