PURPOSE: To detach a core drill main body simply and quickly when chips are jammed, by a core drill for drilling concrete, etc., to form a large aperture wherein a torque transmitting member is provided on a shank movably in the axial direction and it is energized so as to engage with the core drill main body.

CONSTITUTION: A core drill 1 comprises a cylindrical core drill main body 2 and a center drill 3 arranged in it concentrically. The core drill main body 2 and the center drill 3 are mounted on a shank 4 detachably. The torque of the shank 4 is transmitted to the core drill main body 2 through a torque transmitting member 5. In this case, the torque transmitting member 5 is arranged on the shank 4 movably in the axial direction and energized toward the side of the core drill main body 2 by a coil spring 6. When chips are jammed in the core drill main body 2 at the time of drilling of a concrete, a pin setting/ detaching ring 5B is pulled so as to pull out a torque transmitting pin 5A from the core drill main body 2.