To more accurately control a pump output of a compressor.

An air conditioning system has first/second heat exchangers 14, 18 each set up outside/inside an occupant cabin respectively, first/second fluid passages 22, 24 each connecting between the heat exchangers, an expander 16 and accumulator 20 each positioned in the fluid passages, an electronically controlled variable stroke compressor making pump output to the second fluid passage along the first direction X successively passing through the first heat exchanger, expander, second heat exchanger, and the accumulator or along the second direction Y successively passing through the second heat exchanger, expander, first heat exchanger and the accumulator, an inverse flow means 32 controlling the flow direction of a fluid, detection means 36 to 48 outputting detection signals, and control means 26, 30 controlling a stroke of the compressor in accordance with the detection signals.