Tubes extend in a first direction and are stacked in a second direction that is perpendicular to the first direction. A side plate is located on an outer side of the tubes in the second direction. A core plate extends in the second direction, and longitudinal end portions of the tubes are joined to the core plate. A through-hole extends through a bent portion of a holding claw of the core plate. A projection is formed in a side plate end portion of the side plate to project in the first direction. The projection is inserted through the through-hole of the holding claw.