PURPOSE: To operate an air conditioner by a capacity corresponding to an air conditioning load by operating a compressor in frequency based on an output from a frequency converter when the operation current value of the compressor becomes a predetermined value or larger.

CONSTITUTION: An air conditioner detects the operating current of a compressor during an operation in step 27. When the value is 16∼18A, a power source frequency supplied to the compressor at this time is set to the maximum power source frequency in step 32, and it is returned to step 21. When it is 16A or lower, the maximum power source frequency is set to 180Hz in step 31, and it is returned to step 21. When thus returned, the frequency fed from steps 24, 25 to step 26 is based on the power source frequency of the compressor.