The heat exchanger has tubes and a header tank that is located at an end of the tubes in a longitudinal direction and communicates with the tubes. The header tank has a core plate that connects to the tubes and a tank body that is fixed to the core plate. The core plate has a tube connection surface, a sealing surface, and an inclined surface that connects the tube connection surface and the sealing surface with each other. A distance between the tube connection surface and an end surface of the tubes in the longitudinal direction is different from a distance between the sealing surface and the end surface in the longitudinal direction by disposing the inclined surface to incline with respect to the longitudinal direction. The tubes connect to the tube connection surface and the inclined surface in a condition of being inserted to the tube connection surface and the inclined surface.