To fix, in a boom type earth drill mounted on a crawler crane, a rotary frame carrying a rotary table for driving a kelly-bar and a front frame in such a manner that both the frames can be fixed at any angles, that is within any work radius.

In an earth drill a kelly-bar is suspended from the forward end of a boom which is vertically-swingably mounted to a top swivel body mounted on a lower traveling body with crawlers so as to be swiveled, and a drilling bucket is mounted to the lower end of the kelly-bar. In this case a rotary table 2 for driving the kelly-bar is rotatably connected to the top end of a front frame 3 by a pin 5. Further the rotary frame 2 and front frame 3 are connected by an hydraulic cylinder 7 mounted on the frame 3, and angles of the rotary frame 2 at the time the kelly-bar is inserted and the frame 3 takes a horizontal posture at the time of excavation work and at the time of auxiliary suspension work are controlled by expanding and contracting the cylinder 7.