PURPOSE: To protect a motor and control circuit thereof from burning by employing a heat sensitive element responsive to outer air temperature as a reference value setting means for means which stops a motor when the temperature at a heating part in a motor control circuit exceeds a reference value.

CONSTITUTION: A predetermined power supply voltage Vss is divided through resistors R4 and R5 where the resistor R4 is connected in parallel with a thermister Th 2 thus constituting a variable voltage setting circuit 1. The thermister 2 is fixed at a point not subjected to the temperature at a heating part in a motor control circuit 60 but subjected to outer air temperature. A temperature detecting means 52 comprising a thermister Th 1 and a resistor R3 outputs a signal corresponding to the temperature of the motor control circuit 60. Differential input voltage (V+-V-) to a forcible motor stop means, i.e., a comparator IC1, varies with the outer air temperature. When the outer air temperature is low, overload withstanding time is prolonged and when the outer air temperature increases to reach a threshold, the motor is stopped immediately. According to the constitution, overheat of the motor and the control circuit is controlled efficiently.