To rupture a torque transmitting piece by automatically imparting impact force to a rotary shaft when reaching the prescribed depth by providing an actuating means for interlocking with a means for detecting that a fastener with a drill reaches the prescribed depth and releasing a striking body existing in a standby position by being energized by a spring means.

In this rotary tool, a long size rotary shaft 31 is connected to a motor-driven screw driver 30, and a socket wrench 33 is replaceably installed in a connecting metal fitting 32 of a tip part. A hole depth detecting device 50 is installed on an outside wall of a tip part of a guide cylinder 34. When a boring member 2 reaches a prescribed position, a contactor 60 is relatively pushed up by abutting on a fastening object member. Then, a striking body 37 existing in a standby position is released from locking by a hook 44 to be forcibly pressed to the tip side by spring pressure so that the striking body 37 abuts on a strike receiving body 35 to instantaneously impart impact force. Thus, a torque transmitting piece of the boring member 2 ruptures, so that the fastening object member is fixed to a support member.