A temperature sensor is located close to each of a plurality of switching elements. Each of the elements opens and closes a current supplying line from a power supply to a three phase SR motor. A generating circuit of a instruction value for the driving current of the motor generates a target value (It) of the driving current so as to achieve a requested power of the motor and an allowable value of the driving current on the basis of the highest temperature sensed by the temperature sensors. The circuit outputs the target value as an instruction value of the driving current when the target value is smaller than the allowable value and outputs the allowable value as an instruction value of the driving current when the target value is greater than the allowable value.