A heat exchanger includes an outer packaging member. The outer packaging member is configured to allow a heat transfer medium flowed to an inside of the outer packaging member from a heat transfer medium inlet to pass through the inside and flow out from a heat transfer medium outlet. The outer packaging member is made of outer packaging laminate materials each including a metal heat transfer layer and a resin thermal fusion layer provided on one surface of the heat transfer layer. The outer packaging laminate materials are superimposed one on the other. The thermal fusion layers are integrally bonded along peripheral edge portions of the outer packaging laminate materials. The heat transfer layer and the thermal fusion layer of the outer packaging laminate material are laminated via an inner adhesive agent layer made of an acid-modified polyolefin-based adhesive agent containing an acid-modified polyolefin-based resin.