To exhibit temperature control characteristic equal to a heater unit with a temperature conditioning guide even without providing it by bending the extreme end part of an air mix door by an angle so that the extreme end part is along the inner wall of a unit case when the air mix door is positioned so as to fully close a heat exchanger.

Air from an intake unit is introduced into a heater unit 10 after being cooled and dehumidified in an evaporator, and a heater core 3 is provided in the unit case 2 of the heater unit 10 so as to have a bypass. In the vicinity of the heater core 3, a hot air passage 5 and a cold air passage 6 are formed, and an air mix door 20 is rotationally movably fitted to the branch point of the hot air passage 5 and the cold air passage 6 in front of the heater core 3. The extreme end part 20a of the air mix door 20 is bent on the cold air passage 6 side, and hence even at the same opening of the air mix door as a customary heater unit with a temperature conditioning guide, the cold air passage 6 can be narrowed so as to reduce an air quantity on the cold air side.