PURPOSE: To provide a positive control over a circulation flow rate of refrigerant and perform an operation of a compressor under the most efficient manner by a method wherein the number of revolution is controlled in such a way as a degree of over-heating of the refrigerant is kept within a specified limited range and an amount of distribution of the refrigerant is controlled in response to a rate of dispersion calculated in reference to a difference between a room temperature and a set room temperature and a capacity of room.

CONSTITUTION: A refrigerant temperature sensor 25 and a refrigerant pressure sensor 26 may detect a refrigerant temperature and a refrigerant pressure just before the refrigerant is sucked into compressors 2A and 2B and the temperature and the pressure are inputted to a control part 30. At the control part 30, a degree of over-heating of the refrigerant is calculated in reference to the refrigerant temperature and the refrigerant pressure, and then the number of revolution of each of the compressors 2A and 2B is controlled in such a way as the degree of over-heating is kept within a specified restricted range. Since the amount of distribution of the refrigerant supplied from the compressors 2A and 2B in respect to a plurality of indoor heat exchangers is controlled by at least a rate of distribution set by a room temperature of each of the rooms, a difference between the room temperature and a set room temperature and a room capacity, so that it is possible to perform a positive control over a circulating flow rate of the refrigerant and perform an operation of the compressors under the most efficient state.