A heat exchanger includes: a gas-side port connected to piping for a gaseous refrigerant; a liquid-side port connected to piping for a liquid refrigerant; a refrigerant path that links the gas-side port to the liquid-side port; at least four heat exchange part regions that perform heat exchange between air and the refrigerant flowing through the refrigerant path; and a branching and merging part that branches and merges the refrigerant path to connect the heat exchange part regions in series between the gas-side port and the liquid-side port through the refrigerant path. The heat exchange part regions are connected to each other through the branching and merging part so as to allow the number of refrigerant paths provided in the heat exchange part region near the gas-side port to be greater than the number of refrigerant paths provided in the heat exchange part region near the liquid-side port.