A heat exchanger includes tubes which are arranged in parallel and through which a fluid for heating air flows. Fins which are joined to the tubes. The tubes and the fins are arranged to form three or more heating parts and at least two bypass passages each of which is provided between adjacent heating parts, through which the air passes without exchanging heat with the thermal fluid. First and second tank parts are arranged at two longitudinal ends of the tubes and extend across the bypass passages and the heating parts. The bypass passages and the heating parts are arranged perpendicular to an air flow direction. The heating heat exchanger is disposed in an air conditioning case down stream from an evaporator. The air conditioning case is separated into two air outlets. Cold air from the bypass passages and hot air from the heating parts are mixed prior to being blown through the air outlets.