To enhance the workability and handleability of a disc grinder or the like by downsizing a power transmission part because there is a problem that, in a disc grinder where the rotation axis of a spindle intersects the motor axis of a power motor, a bevel gear is used for converting a power transmission direction while decelerating rotative power, however, the diameter of the bevel gear is relatively large, thereby the size of a gear head is increased, and workability is degraded.

A power transmission part 3 is downsized by using an outer rotor type electric motor 10 capable of outputting low-speed rotation and high torque as a drive source, and interposing universal joints 12, 13 instead of conventional bevel gears between its output shaft 10c and a spindle 14.