To easily and surely perform the placing of concrete to a horizontal space formed in a structure.

A concrete discharge port 11 is arranged in the upper part on one end side of a steel shell 3. High fluid concrete C is fed from a concrete injecting device 13 to a concrete hose 12, and the high fluid concrete C is discharged through the concrete discharge port 11 and carried into the space S between an outer cylinder 1 and an inner cylinder 2, and the high fluid concrete C is filled into the horizontal space S1 of a bottom plate part 4 from one end side of the steel sheath 3. The concrete discharge port 11 is successively moved to the other end side of the steel shell 3 at prescribed time intervals.