To make improvement so that expansile blades can be opened certainly for expansion when an excavation rod is propelled for digging to a specified depth.

In the present opening/shutting device for expansile blade of an excavation rod, an expansile blade holder 5 is held, being coaxial with the digging rod, at the lower end of the rod so that both of the members can be turned relatively in normal and reverse rotations within a fixed angle of rotation, a plurality of expansile blades 3 are held at the holder 5 so that they can be swung freely toward the inside for contraction for shutting on an occasion of normal roation of the excavation rod and toward the outside for expansion for opening on an occasion of reverse rotation respectively in positional relations wherein resistance from earth can be received, and a driving member that swings the expansile blades 3 so that the tips of the blades can cut into unprocessed earth by means of above-mentioned relative reverse roations of the rod is provided in projection at the above-mentioned excavation rod.