A first inverter and a second inverter supply two coil sets forming a three-phase motor with AC voltages, which are the same in amplitude but shifted by 30° in phase. Current detectors detect phase currents supplied from the inverters to the coil sets. Temperature estimation sections estimate temperatures of the inverters or the coil sets based on an integration value of the phase current detection values. A current command value limitation section limits upper limits of current command values of both coil sets based on the estimated temperatures Tm1 and Tm2. Thus, the inverters and the coils sets are protected from overheating without increasing torque ripple.