A heat exchanger comprising: a header (50, 50a~h, 60) extending in a horizontal direction; and a plurality of heat transfer tubes (31, 31a~c) extending in a direction that crosses the horizontal direction in which the header extends, disposed side by side in a longitudinal direction of the header, and connected to the header, wherein the header includes a first space (52a, 62b) allowing a refrigerant to flow in a first direction along the longitudinal direction of the header, a second space (52b, 62a) allowing the refrigerant to flow in a second direction that is a direction along the longitudinal direction of the header and that is a direction opposite to the first direction, the second space provided so as to include a portion that is disposed side by side with the first space in the horizontal direction, a circulation member (53, 53a~c, 63) extending so as to separate the first space and the second space from each other while extending in the longitudinal direction of the header, a first communication port (55, 65) allowing the first space and the second space to communicate with each other in the header, a second communication port (54, 64) allowing the first space and the second space to communicate with each other in the header at a position in the second direction with respect to the first communication port, and an inflow port (20a, 19a) allowing the refrigerant to flow into the header, and wherein the first space and/or the second space is directly or indirectly connected to the heat transfer tubes wherein a tilt angle with respect to a vertical direction, which is a direction in which the plurality of heat transfer tubes extend, is less than or equal to 45 degrees. a header (50, 50a~h, 60) extending in a horizontal direction; and a plurality of heat transfer tubes (31, 31a~c) extending in a direction that crosses the horizontal direction in which the header extends, disposed side by side in a longitudinal direction of the header, and connected to the header, wherein the header includes a first space (52a, 62b) allowing a refrigerant to flow in a first direction along the longitudinal direction of the header, a second space (52b, 62a) allowing the refrigerant to flow in a second direction that is a direction along the longitudinal direction of the header and that is a direction opposite to the first direction, the second space provided so as to include a portion that is disposed side by side with the first space in the horizontal direction, a circulation member (53, 53a~c, 63) extending so as to separate the first space and the second space from each other while extending in the longitudinal direction of the header, a first communication port (55, 65) allowing the first space and the second space to communicate with each other in the header, a second communication port (54, 64) allowing the first space and the second space to communicate with each other in the header at a position in the second direction with respect to the first communication port, and an inflow port (20a, 19a) allowing the refrigerant to flow into the header, and wherein the first space and/or the second space is directly or indirectly connected to the heat transfer tubes wherein a tilt angle with respect to a vertical direction, which is a direction in which the plurality of heat transfer tubes extend, is less than or equal to 45 degrees.