A vehicle includes an internal combustion engine 1 and a rotating electric machine 5 as drive power sources and drives a wheel using a driving force of the internal combustion engine 1 and/or the rotating electric machine 5. A diagnostic control unit 700 diagnoses the vehicle while controlling the same. The diagnostic control unit 700 shifts an operating point of the internal combustion engine 1 to a plurality of diagnostic operating points to diagnose a catalyst or an oxygen sensor. Meantime, the diagnostic control unit 700 compensates for an excess or a deficiency in the driving force of the internal combustion engine 1 accompanied by the shift of the operating point by letting the rotating electric machine 5 perform a power running or regeneration operation.