PURPOSE: To determined humidity in accordance with the data indicating the relation between the deviation in the number of revolutions and humidity and to eliminate the need for moisture sensors, etc. by measuring the number of revolutions of a fan motor in the dry state and state of a room heat exchanger.

CONSTITUTION: The number of revolutions of a room fan motor 10 which is a driving motor for a room fan 9 in a dry state is measured and this is stored as a reference number of revolutions beforehand in the ROM in a CPU11 which is a main controlling part of an air conditioner. The number of revolutions of the motor 10 during operation of cooling is measured with a revolution sensor 12, and is inputted to the CPU11 via an A/D converter 13. The room temp. is measured with a temp. sensor 14, and further the temp. of a room heat exchanger 1 is measured with other temp. sensor, respectively, and these are inputted to the CPU11 via the converter 13. These data are arithmetically processed in the CPU11, whereby humidity is determined.