A heat exchanger includes: a partition wall that separates two fluids of different temperature; and multiple plate-shaped fins formed on at least one surface of the partition wall and each having a pair of heat transfer surfaces. The partition wall and the multiple fins are made of a same metal material to constitute an integrally molded product. The multiple fins each have a curved part and are arranged to be spaced from one another in a direction intersecting with the pair of heat transfer surfaces. Each heat transfer surface of the pair of heat transfer surfaces is formed with multiple grooves having a depth of 100 μm to 400 μm in a thickness direction of each fin.