A heat exchanger is configured to exchange heat between a heat medium and an air. The heat exchanger includes a tube through which the heat medium flows therein, and a fin that is formed by bending a metal plate and that is brazed to a surface of the tube. The fin includes a louver. The surface of the tube defines an introducing groove configured to introduce a brazing material melted at brazing from a connecting portion between the tube and the fin to an other portion.