A heat exchanger includes: each of the fin plates having a V shaped or trapezoid corrugated shape, and including top walls positioned at top portions of the corrugated shape, bottom walls positioned at bottom portions of the corrugated shape, and foot portions each connecting one of the top walls and one of the bottom walls, each of the foot portions having a rectangular corrugated shape along one of the top walls and one of the bottom walls, and including stepped walls formed at a predetermined interval along the one of the top walls and the one of the bottom walls, and opening portions each formed in one of the stepped walls, and being an elongated through holes having a width equal to or smaller than a thickness of one of the fin plates.