PURPOSE: To compute highly accurate presumed value even without an outside air sensor and a solar radiation sensor for carrying out comfortable control by preparing a correction term based on the quantity of feedback for severally making correction to each detected or presumed value used as a parameter.

CONSTITUTION: Signals issued from an outside air temperature detecting sensor, an indoor temperature detecting sensor, a blowing out temperature detecting sensor and a direct irradiating sensor are inputted into a control unit 30. In the case where the specified detecting sensor among the above sensors is not used as input, for instance, the opening of an air mixing door for adjusting the blowing out air temperature is controlled. In this case, an observer 37 is a presumption model for presuming the quantity of solar radiation being the function of a predetermined control object system 38. In an actual system (control object) 38 and the observer 37, their feedback value functions so as to show the influence of their input errors. An expression being its correction term removes its variation component by a low path filter 42 to converge the presumed values.