An air compressor (12b) starts to operate when fuel to an internal combustion engine (1) is cut off and the engine (1) and a transmission (4) are directly engaged. Upon receiving a drive request signal, a controller (21) outputs a lockup clutch disengaging request. The controller (21) resumes fuel supply and starts driving of the air compressor (12b) only when it is confirmed that the lockup clutch (3) has been disengaged, thereby preventing a recovery shock from generating due to resumption of fuel supply during the lockup clutch (3) being in the engaged state.