A host controller is incorporated with a plurality of different pieces of control software which are applicable to a plurality of destinations for a cooling blower to cool a main battery incorporated in a vehicle. The host controller transmits a destination-signal request pattern for requesting a destination signal pattern to specify the determinations for the cooling blower, to a motor control device by a pulse width modulation (PWM) signal. Upon receiving the destination-signal request pattern, the motor control device transmits the destination signal pattern to the host controller. The host controller specifies one of the destinations for the cooling blower from the received destination signal pattern, and then changes over the control software to the control software applicable to the specified destination for the cooling blower.