A driving force generated by an engine is transmitted to driving wheels (not shown) via an automatic transmission. The engine is provided with an electronically controlled throttle body and the like. An E-ECU performs cooperative control when necessary, so that an output of the engine is obtained in accordance with a load applied thereto. On the other hand, the automatic transmission is provided with a torque converter. Even in the case where the aforementioned predetermined condition has been fulfilled in a T-ECU, if the E-ECU detects a deterioration in performance of the electronically controlled throttle body or the like, the performance of neutral control is prohibited.