To improve the accuracy of detecting the vertical moving speed and press-fitting depth of a casing at the time of press-fitting the casing into the ground or pulling it out by a ground improving machine, and make construction speed high so as to improve work efficiency.

A rod end part 16a of a hydraulic cylinder 16 for vertical oscillation, and a rod end part 17a of a hydraulic cylinder 17 for vertical stroke are connected to an upper bracket 19 by a pin 18. A vibro hammer 14 is connected to an intermediate bracket 20 by a pin 21, and the intermediate bracket 20 is connected to a tube 16b of the hydraulic cylinder 16 for vertical oscillation. The upper bracket 19 and intermediate bracket 20 are respectively supported in a vertically slidable state to a leader 12. Another hydraulic cylinder 22 is retrorsely provided at the lower part of the hydraulic cylinder 17 for vertical stroke and integrated, and its rod end part 22a is connected to a lower bracket 23, fixedly provided at the lower end part of the leader 12, by a pin 24.