PURPOSE: To realize efficient performance of air conditioning by letting a part or the whole of exhaust gas bypass a turbocompressor driving exhaust turbine by means of a bypass valve when high pressure in refrigerating cycle is raised above the set value.

CONSTITUTION: An exhaust turbine 9 connected to a turbocompressor 11 is driven by means of exhaust gas of an engine 7 to form a refrigerating cycle for circulation through a condenser 12, expansion valve 13 and an evaporator 14, and air conditioning in a car is performed. At this point, when engine speed is increased and the output of a turbocompressor 11 is augmented and further the high pressure side pressure of the refrigerating cycle is raised above the set value, a high pressure control device 16 is operated to open an exhaust gas bypass valve 15. Then, through letting a part or the whole of the exhaust gas bypass, control is performed so as to lower the high pressure side pressure to a predetermined one. Air conditioning in the car can be thus performed efficiently without increasing an engine load and a trouble of the compressor can be prevented previously.