PURPOSE: To provide a nonconductive clutch device by which the occurrence of impact vibration or an impact sound of a motor-driven rotary tool can be prevented by improving a shape of a clutch cam surface, and preventing spring resiliency acting on the clutch cam surface from colliding suddenly with the surface when clutch operation is carried out.

CONSTITUTION: A driven shaft 26 is connected to an output shaft 14 of an electric motor through a planetary gear mechanism 12, and an internal gear 20 meshing with a planetary gear 28 is arranged rotatably freely in a cylindrical gripping part casing 28 to surround the planetary gear mechanism 12. A steel ball 30 to carry out clutch operation is contacted with an outside surface of a blocked-up bottom surface part of the internal gear 20 while holding spring resiliency in the thrust direction, and a projecting part 22 which projects at a necessary inclination successively in the direction with which the steel ball contacts when the driven shaft 26 is rotated forward and is used as a clutch cam surface to become a gentle inclination gradually thereafter, is arranged on the outside surface of the blocked-up bottom surface part of the internal gear 20 with which this steel ball 30 contacts.