A heat exchanger includes an apparatus body, a motor, an air-exhaust fan casing, an air-supply fan casing, heat exchanging devices, an air-supply air-flow path, and an air-exhaust air-flow path. A first stacking pitch of heat transfer plates in the heat exchanging devices placed at positions other than that immediately after an outdoor suction port in the air-supply air-flow path and at positions other than that immediately after a indoor suction port in the air-exhaust air-flow path is smaller than a second stacking pitch of heat transfer plates in the heat exchanging devices immediately after the outdoor suction port in the air-supply air-flow path and immediately after the indoor suction port in the air-exhaust air-flow path.