A heat exchanger includes tubes layered in a layering direction, a side plate arranged most outside of the tubes in the layering direction, and a core plate extending in the layering direction. The side plate has an end portion in a longitudinal direction, and the core plate has a wall portion extending in the longitudinal direction. The end portion of the side plate has a brazing section brazed to an outer face of the wall portion of the core plate, and the end portion of the side plate has a through hole located in the brazing section.