The operation of air compressor is controlled to control engine performance to thereby improve the performance of the vehicle. A compressor (4) driven by the engine (3) of a vehicle and supplying compressed air to loads (51-54) is controlled by an ECU (2), the loaded state and the unloaded state of the compressor (4) are switched between each other according to the requirements from the loads (51-54), and when the vehicle requires braking force, the compressor (4) is set to the loaded state irrespective of the requirements from the loads (51-54).
