PURPOSE: To provide a stable a coolant operation in case of transmission, reduce a load of a compressor and improve a reliability of the compressor by a method wherein a degree of opening of an expansion valve is set in advance for every operation mode of a cooling operation and a heating operation, thereby a stability of coolant cycle in case of transmission is made.

CONSTITUTION: Indoor unit control devices 9 and 19 may detect surrounding temperatures of evaporators 5 and 6 with temperature sensors 12 and 13 and send them to an outdoor unit control device 8. Simultaneously, an operating information of an indoor unit is sent. In the outdoor unit control device 8, information from the indoor unit and the surrounding temperature of a condensor 2 are detected by a temperature sensor 11. Degrees of opening of expansion valves 3 and 4 are controlled in response to these information. When one indoor unit is stopped during operation of two units, the expansion valve of the stopped indoor unit is fully closed. The remaining expansion valve for indoor unit shows temporarily a predetermined degree of opening in such a way as a variation of refrigerating cycle is restricted as less possible. A predetermined degree of opening is larger as a suction air temperature for the condensor is large, and it is set such that it becomes a larger value as the suction air temperature for the evaporator is increased. That is, a predetermined degree of opening is set large and an amount of circulated coolant is increased to enable a rapid increasing of condensing pressure to be restricted.