PURPOSE: To realize efficient performance of air conditioning without giving load change to an engine by providing an exhaust turbine which drives a turbocompressor of a refrigerating cycle and opening or closing an exhaust gas bypass valve correspondingly to a change in the temperature of a compartment.

CONSTITUTION: A refrigerating cycle is formed for circulation by a refrigerant through a condenser 15, expansion valve 16 and an evaporator 17 by means of a turbocompressor 14 connected to an exhaust turbine 12 driven by an exhaust gas of an engine 10, and air conditioning is performed. When the temperature in a compartment is lowered and a temperature sensing cylinder 19 detects the temperature below the set value, a control device 20 is operated to open an exhaust gas bypass valve 18 to let a part or the whole of the exhaust gas bypass. Then the output of the turbocompressor 14 is reduced to control the temperature of the compartment at comfortable one. Thus, efficient air conditioning can be performed without augmenting an engine load, and further change in the temperature of the compartment can be lessened without giving a load change to the engine.