PURPOSE: To obtain a large supporting force, by securely swelling bags.

CONSTITUTION: A cloth bag body 1 is fitted to the upper and lower positions thereof on the outer periphery of the lower part of a pile 5. Weak bands 3 are wound up on the periphery of the bag body 1 so that the band is brocken when a specified injection pressure is acted on the bag body 1. Further, an injection pipe 4 is provided so as to communicate with the lower part of bag body. when the pile is applied to a supporting layer including gravels and gravelly soil, slime and sandy gravel piling on the excavated bottom face is reduced and the bad body is swelled from the lower part. In this way, it is enlarged and expanded while removing upward floating and settling sandy gravel.