To compensate for the defficiency of the absorption power of a brake by applying a load on an engine by continuously operating an air compressor without making the air compressor non-operative at the time of the deceleration of a vehicle.

A controller for an air compressor comprises an air compressor 2 driven by an engine 1 mounted to a vehicle so as to compress air, a main air tank 6 and a sub-air tank 7 connected in parallel with the air compressor 2 so as to store compressed air, a changeover valve 9 having a first position where the compressed air from the air compressor 2 is supplied the sub-air tank 7 and a control means 12 for use in the control of the changeover valve 9. The control means 12 changes over the changeover valve 9 to the first position where the compressed air from the air compressor 2 is supplied to the main air tank 6 at the time of running except the deceleration time of the vehicle and changed over the change valve 9 to a second position where the compressed air from the air compressor 2 is supplied to the sub-air tank 7.