PURPOSE: To keep the sensitivity of receiving an infrared ray radiation signal from a remote control device at a level higher than a predetermined value irrespective of the room temperature by a method wherein a heat generating fixed resistor is provided near an amplifying IC within a light receiving section and the surface temperature of the IC is increased by heat discharged from the register.

CONSTITUTION: The relationship between a set temperature voltage V2 impressed upon a non-reversible input terminal of a comparator 10 and a sucked air temperature convertion voltage V1 impressed upon a non-reversible input terminal of the comparator is such that: when V1<V2, the output signal 10a of the comparator 10 goes high to enable a transistor 11 in the light receiving section 4 to turn ON and a load current 7a flows through the heat generating fixed resistor 7 so as to make the latter generate heat so that the light receiving sensitivity of the light receiving amplifying IC 4b increases since the resistor 7 is arranged near the IC; and when V1>V2, the output signal 10a goes low through the resistor 7 but since, in this condition, the temperature of sucked air in the air conditioner is high and also the temperature of the light receiving section is high, the temperature of the IC 4b is kept at a high level so that the light receiving sensitivity of the light receiving section does not go bad.