To prevent an electric motor from overheating by controlling that a main control section compares a specified target current value with a limit current value and whichever smaller is chosen as an energizing current for an electric motor to control power supply.

A main control section 2 actuates target current value specifying function to specify a target current value for an electric motor 1A according to vehicle speed information sent from a vehicle speed sensor 11 and pedal force information sent from a pedal force sensor 12. Next, limit current value specifying function is actuated and the limit current value is specified according to a mean current value calculated from current values detected with a current sensor 14 at specified time intervals. The specified target current value is compared with the limit current value and whichever smaller is chosen as an energizing current for the electric motor 1A to control power supply. Thus, the electric motor 1A is prevented from overheating.