PURPOSE: To reduce load in the case of engine output being lowered so as to prevent the lowering of traveling performance by stopping the driving of an air conditioner when the vehicle speed does not reach the fixed value even after the lapse of the specified time in the fully opened state of throttle opening.

CONSTITUTION: The engine control part 50 of a control means 48 receives the signals of a throttle sensor 32, an intake air temperature sensor 34, and the like so as to control the compressor 26 of an air conditioner 6 by a fuel injection valve 40 and an air-conditioning control part 54. When the vehicle speed of a vehicle speed sensor 52 does not reach the fixed value even after the lapse of the specified time in the fully opened state or throttle opening, the engine control part 50 of the control means 48 operates the air-conditioning control part 54 so as to stop the driving of the air conditioner 6. Load to an engine is thereby reduced when engine output is lowered so as to improve traveling performance and have an advantage from the cost point of view.