A heat exchanger includes a plurality of flat tubes. The flat tubes have a pair of tube sheets facing each other and joined together. The tube sheets have a flat part, a recess part, and a cylindrical tank. The tube sheet is one of a first tube sheet and a second tube sheet. The first tube sheet has a first type of tank. The second tube sheet has the first type of tank and a second type of tank. Identifiers are provided at each end of the second tube sheet. The identifiers distinguishing the second tube sheet from the first tube sheet when viewed from externally of the stacked flat tubes. A mark provided at one of the identifiers of the second tube sheet.