A self-holding termination determination section has an overheat protection map that defines a relationship between a current value and a maximum temperature of a protected portion to which a current value is applied, and sets a limit temperature corresponding to a required current value at next start time based on the map. The self-holding termination determination section calculates, as an evaluation temperature, temperature obtained by adding a performance assurance upper limit temperature, which assures output performance of a motor at the next start time, to the sum of temperature rises. In a next time performance determination process, if the evaluation temperature for all protected portions has fallen below the limit temperature, the self-holding termination determination section determines that a performance assurance condition is met, and terminates power self-holding based on at least the fact that the performance assurance condition is met.