PURPOSE: To obtain optimum room temp. most suitable for health by controlling room temp. maintaining optimum difference between the outdoor temp. based upon the outdoor temp. information.

CONSTITUTION: Temp. sensor 3 which detects outdoor temp. is installed on the outside of the house 1, which comprises surface wave oscillator consisting of surface acoustic wave delay line 4 and amplifier 5. Outdoor temp. is detected at sensor 3, and oscillation frequency corresponding with the detected temp. is outputted, which is received by receiver 6 and output corresponding to the outdoor temp. is generated. Under the system, temp. of heat generated at air conditioner body 2 is controlled maintaining a prescribed difference between the outdoor temp. Accordingly, room temp. inside of the house 1 is always maintained keeping optimum difference with outdoor temp.