A heat exchanger includes tubes arranged in a stacking direction and a tank connected to the tubes. A tube of the tubes has a pair of flat portions having flat plate shapes facing each other, and a curved portion connecting ends of the pair of flat portions. The tank includes a plate having insertion holes into which the tubes are inserted, and container. The plate has a first portion along a longitudinal direction of the tubes, and a second portion extending from an end of the first portion toward the container. When the plate is viewed in the stacking direction, a boundary between the first portion and the second portion is shifted from a boundary between each of the pair of flat portions and the curved portion toward the pair of flat portions.