PURPOSE: To enable to realize the adequate and effective air-conditioning which complies with user's selection by a method wherein the difference between the set valve of temperature and room temperature is detected with every predetermined period and the operating capacity of a compressor and at the same time the partition ratio of refrigerant are changed based upon said temperature difference.

CONSTITUTION: At the first period of operation, the differences D14 and D15 between the set values of temperature and actual temperatures of the respective air-conditioned rooms are inputted from indoor control units 14 and 15 to an outdoor control unit 16, which calculates Dt= D14-D15 and set the valves of control voltages B8 and B9 in order to determined the openings of proportional control valves 8 and 9 and at the same time calculates the rotational frequency (f) to be increased or decreased based upon Dt in order to determine the operating capacity of a compressor 4. After that, at intervals of the predetermined period, Dt, B8 and B9 are calculated so as to determine the openings of the proportional control valves 8 and 9 in order to determined the partition ratio of refrigerant and change the operating capacity of the compressor 4. By controlling based upon the difference between the set temperature and actual temperature, the adequate operation complying with user's selection and effective operation because of the change of the operating capacity of the compressor can be performed.