Legend said this well was made by by Kobo Daishi, the founder of Shingon Buddhism. In 809, the wife of Sugiura Kichinojo was make a living with very short of money after her husband's death. One day, a monk visited her, and she served rice soup. The monk found out there is no salt in the soup, and asked her why. She said salt was too expensive to buy. The monk put his stuff on the ground and prayed, then from the spots salt water started springing. She found out that monk was Kobo Daishi, Kukai.
This is the popular story of Kobo Daishi in Chiba prefecture.