A heat exchanger according to the present invention has a plurality of tubes, header tanks and a support. Fluid flows through the plurality of tubes. The header tanks have a core plate and a tank body, and are disposed at longitudinal end portions of the plurality of tubes in such a manner to be communicated with internal spaces of the plurality of tubes. The core plate has approximately arc-shaped cross-section of which both side fringes are fixed onto the tank body and of which a middle portion fixes the longitudinal end portions of the plurality of tubes therein and bulges with respect to the both side fringes toward the plurality of tubes. The tank body and the core plate form an internal space of each of the header tanks. The support retains an interval between the both side fringes.