HEAT MEDIUM HEATING DEVICE AND VEHICLE AIR CONDITIONING APPARATUS USING THE SAME

In a heating-medium heating unit (10) equipped with a first heating-medium circulation box (A) and a second heating-medium circulation box (B) which are in close contact with both surfaces of a PTC heater (40), in which heating-medium circulation passages (33, 54) are formed in the interior, and which are joined to each other in a liquidtight manner, wherein joining surfaces (M1 to M4) are sealed with liquid gaskets, the heating-medium circulation passages (33, 54) are provided with joining-surface cooling channels (C1, C2) that cool the joining surface (M1) which is sealed with a liquid gasket and on which the heat from the PTC heater (40) acts. The joining-surface cooling channels (C1, C2) are provided at positions closer to the joining surface (M1) than to the PTC heater (40).