To provide a multi-chamber type air conditioner which is provided with a bypass passage through an expansion valve between a delivery side and a suction side of a plurality of compressors, can keep high pressure higher than a fixed value in a heating operation at low fresh air temperature and improve heating capacity.

The bypass passage 10a is installed through the expansion valve 10 between a delivery side a and a suction side b of a plurality of the compressors 3a, 3b, 3c which are connected in parallel and have difference capacitance. Pressure sensors 11a, 11b which detect high pressure and low pressure are respectively installed at the delivery side a and the suction side b. When the compressor is operated with minimum capacity or more in a heating operation at low fresh air temperature and the low pressure detected by the pressure sensor 11b becomes a prescribed bottom value or less, an opening of the expansion valve 10 is controlled such that the compression ratio of the compressor required from the high pressure and the low pressure becomes a target value set beforehand. Afterwards, when the low pressure reaches a prescribed top value or more, the expansion valve 10 is closed, simultaneously the compressor is switched to the compressor with minimum capacity.