PURPOSE: To easily fix a tool holder on a chuck by radially movably providing a fixing element.

CONSTITUTION: When a tool holder 5 is moved onto a chuck 2, a ball 9 makes contact with the outer end of a chuck 4, thereby stopping the movement of a sleeve 6 toward a drilling machine. A user manually pressing the tool holder 5 against the top of the chuck 2 thereby moves a housing 14 toward the drilling device, whereby a spring 16 is compressed to allow a ring 11 to reach the position of an opening 8, resulting in the outward movement of the ball 9 and the disposition of the sleeve 6 at the corresponding part of the chuck 2. Next, by lightly turning the housing 14 by hand relative to the drilling machine, for example, the ball 9 can be engaged with a hole 4. Immediately thereafter, a second ring 12 binds the ball 9 in its inward position and locks it with an opening 4.