The purpose of the present invention is to provide a compact heat exchanger with which the generation of excessive pressure loss can be suppressed and a suitable flow rate can be assured in accordance with the volumetric changes of a fluid due to phase changes. This heat exchanger (1) comprises a flow path (8) which has an inlet (10) into which a fluid (6) flows and an outlet (11) through which the flowed fluid (6) flows out, and in which a phase change from a fluid phase to a gas phase occurs between the inlet (10) and the outlet (11), wherein the inside of the flow path (8) is formed in a resistance shape (12) so that the amount of flow path resistance applied to the flow of the fluid (6) is smaller on the outlet (11) side than the inlet (10) side.