In a vehicle designed so that a driven wheel is driven by uniting an output from an engine and an output from a Rankine cycle system to each other, an accelerator pedal and a throttle valve are connected electrically to each other by a DBW control unit. When an accelerator opening degree (θap) commanded by a driver is increased, a throttle opening degree (θth) is increased by a correcting amount (Δθth) more than a value proportional to the accelerator opening degree (θap), thereby compensating for an output shortage due to a response delay of the output from the Rankine cycle system. When the accelerator opening degree (θap) commanded by the driver is decreased, the throttle opening degree (θth) is decreased by the correcting amount (Δθth) more than the value proportional to the accelerator opening degree (θap), thereby compensating for an output excessiveness due to the response delay of the output from the Rankine cycle system.