To prevent an interference in a bracing base at the time of excavation and extraction.
A kelly-bar 26 is suspended from a main wire 14 from a main winch 12 loaded on a construction equipment body 1, and an excavating tool 28 is installed at the front end of the kelly-bar 26. A sheave is supported rotatably to a bracing base 34 supported to a leader 2 in a manner that the bracing base 34 can be lifted and lowered. A wire 66 from a winch 64 is wound on the sheave while the tip of the wire 66 is connected to a connecting member 68 mounted on the front end side of the kelly-bar 26, and the bracing base 34 is hung dot. A lower-section bracing base 70 stopping the shaking of the kelly-bar 26 is supported on the lower end side of the leader 2 in a manner that the lower-section bracing base 70 can be elevated and brought down.