A finless heat exchanger includes a pair of headers each including a pipe-shaped portion extending in a first direction, and branching portions formed on the pipe-shaped portion, and flat pipes each having a flat sectional shape elongated in one direction, the flat pipes being arrayed in the first direction and connecting the branching portions of the headers. Flat surfaces of adjacent two flat pipes face each other and the adjacent two flat pipes each have a side surface facing a second direction orthogonal to the first direction. The flat pipes connect the branching portions, the side surface of each of the flat pipes has a wave shape, and adjacent flat pipes are prevented from contacting each other. Both the side surfaces are opened so that air flows in from a side corresponding to one side surface in the second direction and flows out from a side in the second direction.