An air conditioning system 1 includes a primary compressor (an engine-driven compressor 6) driven by a primary driving source (an engine 2) and a secondary compressor (a motor-driven compressor 7) driven by a secondary driving source (a motor 3). When a required cooling capability is equal to or greater than a predetermined value, the air conditioning system 1 causes the primary compressor (the engine-driven compressor 6) to be driven by the primary driving source (the engine 2) and adjusts the rotational speed of the secondary compressor (the motor-driven compressor 7), whereas when the required cooling capability is equal to or smaller than the predetermined value, the air conditioning system 1 causes the secondary compressor (the motor-driven compressor 7) to be driven by the secondary driving source (the motor 3) so as to control the rotational speed of the primary compressor (the engine-driven compressor 6).