To avoid a motor from being intermittently stopped by a little temperature change while the rotation control of the motor is maintained.

A thermistor S is provided on the stator side of a motor M to detect a temperature. A comparison unit 11 which compares the detected temperature of the thermistor S with a 1st reference temperature and a 2nd reference temperature higher than the 1st one is provided. The comparison unit 11 outputs off-control signals continuously when the detected temperature is elevated from the 1st reference temperature, and exceeds the 2nd reference temperature and outputs on-control signals continuously when the detected temperature is lowered from the 2nd reference temperature and falls below the 1st reference temperature. A switching unit Q is connected to the comparison unit 11 and the on/off control of the transmission of a rotation control signal Vs to a rotation control unit 7 is carried out in accordance with the on-/off- control signals.