To provide a heat exchanger reduced in weight and cost and increased in heat exchange efficiency.

In this heat exchanger 1, heat is exchanged between a first heat medium flowing through a first heat medium flow passage 11 and a second medium flowing through a second heat medium flow passage 21 without allowing these both media from being brought into direct contact with each other. The first heat medium is a gas, and the second heat medium is a liquid. The first heat medium flow passage 11 through which the gas flows is formed on one or both surfaces of the joined surface of two metal plates 10, 12 joined to each other. The heat medium flow passage 21 through which the liquid flows is formed on at least one surface of a synthetic resin plate 20. The synthetic resin plate 20 is joined to at least one surfaces of the two metal plates 10, 12 joined to each other in such a state that the surface on which the second heat medium flow passage 21 is formed is brought into contact with these one surfaces.