To provide a finless heat exchanger which hardly allows clogging resulting from frost formation to occur and thus reduces the frequency of defrosting operations.

Heat exchanging tubes 11 are of flat shapes having sectional shapes extending in the direction of flow of air that exchanges heat with a refrigerant, and are arranged at intervals in the direction perpendicular to the direction of flow of air. Each interval between heat exchanging tubes 11 adjacent to each other is formed such that the downstream side of the interval is larger than the upstream side in the direction of flow of air. Because of this structure, clogging between the heat exchanging tubes 11 resulting from frost formation hardly occurs. As a result, the number of times of defrosting operation for eliminating frost is reduced, which leads to a reduction in energy consumption.