A machining device includes a rotary cutting tool, and an electric motor as a drive source for rotating the rotary cutting tool. A motor housing of the electric motor is connected to a stationary cover covering the rotary cutting tool. The electric motor is an outer rotor type electric motor includes a stator situated inside of a rotor. A rotor is supported by a motor shaft at a position of output side in the motor axis direction with respect to the stator. The rotor is mounted to the rotor base and is rotatably supported on the stationary cover. The stator is fixed to the motor housing so as to be immovable in the motor axis direction, and is arranged inside of the rotor.