PURPOSE: To accurately detect the temperature of a coil without installing a temperature sensor in the coil by calculating the temperature from the supplied voltage, ON/OFF ratio of the coil current, and coil current itself while considering the correcting values.

CONSTITUTION: An adjustment operating signal PWM processed pulse-width- modulated by a control/evaluation circuit 5 through a line 10 is transmitted to an output switch RLSPV of a coil current circuit 4. The signal PWM includes control information of ON/OFF ratio ppv shape and controls the practical current Ispute flowing in the coil 1 in the circuit 4. As the supplied voltage in the circuit 4, the voltage KL15, that is the battery voltage UKL15 in the control apparatus 9, is employed and the circuit 15 takes in the voltage through a line 11. Moreover, in order to compensate the detected temperature error, balancing adjustment is carried out using the temperature sensor 8, the correcting value TA to the coil temperature is computed and the circuit 15 takes in the result through a line 13. The circuit 15 computes the temperature of the coil 1 from the voltage UKL15, the ON/OFF value ppv of electric current, and the current Ispute while considering the correcting value TA.