A heat exchanger includes: flat pipes each including a passage for refrigerant that are arranged side by side in a predetermined step direction; and a header collecting pipe extending along the predetermined step direction that is connected to the flat pipes. The header collecting pipe includes: a flat pipe-side header forming member; and an opposite-side header forming member facing the flat pipe-side header forming member. The flat pipes are inserted in the flat pipe-side header forming member and an internal space exists between the flat pipe-side header forming member and the opposite-side header forming member. When viewed along the predetermined step direction: the flat pipe-side header forming member has a flat pipe-side curved portion protruding toward the flat pipes and the opposite-side header forming member has an opposite-side curved portion protruding toward a side away from the flat pipes.