A heat exchanger includes tubes and a header tank. The tubes are arranged in parallel with each other, and fluid flows in the tubes. The header tank is disposed at end portions of the tubes in a longitudinal direction of the tubes and extends in a direction in which the tubes are arranged in parallel with each other to communicate with the tubes. The header tank includes a core plate, a resin tank main body part, and a resiliently-deformable sealing member. The tubes are joined to the core plate. The tank main body part is fixed to the core plate. The core plate includes a receiving part at which the sealing member is disposed. The tank main body part is fixed to the core plate with the sealing member clamped between an end part of the tank main body part on the core plate-side and the receiving part. The receiving part is disposed on a farther side from the tubes in the longitudinal direction of the tubes than the end portions of the tubes in the longitudinal direction of the tubes.