An overall loss L during non-execution of intermittent boosting (in ordinary boosting) is calculated from losses L1 and L2 of motors and a loss LC of a boost converter during non-execution of intermittent boosting. The overall loss L during execution of intermittent boosting is calculated from the losses L1 and L2 of the motors and the loss LC of the boost converter during execution of intermittent boosting. A minimum loss-time boosting voltage Vtmp at which the overall loss L provides a minimum loss Ltmp is set to a target voltage VH*. The boost converter is then controlled in a control state corresponding to the minimum loss-time boosting voltage Vtmp.