32 for determining a reference temperature of air to be blown into a rear seat space vb of the vehicle passenger compartment the air temperature control for the rear seat space vb is achieved when the third connecting passage 33c is omitted the inlet of the third connecting passage 33c may be connected with a passage leading to the vent outlet 23 a second air mix door 34 is disposed between outlets of the first and second connecting passages 33a 33b that open to the rear seat air mix chamber 32 so that a proportion of air passing through the first connecting passage 33a is adjustable depending on the position of the second air mix door 34 the door 34 is operative controlled by a second actuator 35 for determine the temperature of air to be blown into the rear seat space vb the rear seat duct 30 is bifurcated into two branch duct portions at a position downstream of the blower 31 a rear seat mode door 36 is disposed between the bifurcated branch duct portions one of which has a central vent outlet 37 facing to the rear seat space vb of the passenger compartment the vent outlet 37 being disposed centrally between two front seats the other branch duct portion is further bifurcated into left and right outlets 38a 38b the rear seat mode door 36 is operated to select the outlet 37 or the outlets 38a 38b through which temperature controlled.