In an air conditioner for automobiles, control unit for performing feedback control of blow off air is constructed in the form of an integral-added optimal regulator (M4) which performs the feedback control on the basis of optimal feedback gain predetermined according to dynamic model(s) of an air conditioning system including the vehicle compartment (M1) and the used air conditioning unit (M2). According to another feature of the present invention, an environmental condition, such as solar radiation to the vehicle compartment (M1), is detected to further accurately control the internal air temperature. In one embodiment, the internal variables including optimal feedback gain of the integral-added optimal regulator (M4) are changed in accordance with the variation in the dynamic model depending on the detected environmental condition. In another embodiment, in addition to the above-mentioned feedback gain, feedforward gain is used so as to finally determine controlled variables of blow off air control unit (M2). Furthermore, according to another feature of the present invention, temperature control may be performed at a plurality of different positions within a vehicle compartment using a plurality of air conditioning units without suffering from interference between a plurality of airflows.