To prevent excess current from being allowed to flow and cause generation of heat and destruction of elements and thereby increase the reliability of the device by detecting the residual voltage of a switching power supply, when a sensorless brushless motor is started again after a short-time stoppage and locking the start-up of the motor.

This device is composed of a brushless motor 101, a switching element section 102, a switching power supply 103, a voltage-detecting means 1, a comparing means 2, a position-detecting means 104, a drive means 105, a rotary speed controlling means 106, and a start-up operating locking means 3. In this case, residual voltage at the time of start-up of the motor is detected by the start-up operation locking means 3, and the rotary speed controlling means 106 is prevented from outputting a motor operation signal, until the output signal of the comparing means 2 becomes a reference value or below.