PURPOSE: To perform agreeable air conditioning from the start of air conditioning operation by a method wherein set temperature is changed based upon the detected result of the difference between room temperature and the set temperature.

CONSTITUTION: Room temperature signals from a room temperature sensor 4 are transmitted through a temperature comparator 5 to compare room temperatures with the set temperature to a room temperature setter 6. When the difference between the initial room temperature (a) and the set temperature (b) exceeds a fixed value (about 5°C), the room temperature setter 6 resets the set temperature (b) to the set temperature (c), which is different from the set temperature (b) by about 2W3°C (higher in case of heating as illustrated in the accompanying figure and lower in case of cooling). When room temperature reaches the OFF point (d) of the set temperature (c), a compressor 7 is turned OFF. The room temperature setter 6 detects the first OFF action of the compressor 7 counting from the start thereof and sets back the set temperature (c) to the original set temperature (b).