PURPOSE: To improve the operativity of setting of the temperature adjustment, by inputting and outputting perirodically output of an inside air temperature sensor into and from a microcomputer and displaying it as a temperature.

CONSTITUTION: The temperature set by a temperature lever 37 is stored in the microcomputer 30 as a reference temperature, the set temperature is displayed on a displayer 42, a lamp is lit and a timer 35 is operated for a prescribed period of time. In a case where the temperature lever 37 is not changed, the temperature display is continued until a prescribed period of time has passed after the temperature lever 37 is stopped. When the room temperature exceeds the prescribed temperature range, the lamp is flickered, and the set temperature is displayed on the displayer 42. After the room temperature falls again within the range, the temperature display continues for a certain period. Thus, using a signal display elements, usually the car interior temperature is monitored, the set temperature is suitably changed to perform favorable temperature control and therefore the operability of temperature control is improved.