A frostless heat exchanger used for an air-source system, comprises: an antifreezing solution supplying device for applying an antifreezing solution having a freezing point lower than a surface temperature of the heat exchanger on a surface of the heat exchanger to form a thin solution film on the surface of the heat exchanger in order to prevent formation of frost on the surface of the heat exchanger when the surface temperature of the heat exchanger drops below a freezing point of water (0° C.), so that the vapor is removed in such a manner that a highly concentrated antifreezing solution and the vapor are mixed together before the vapor becomes a supersaturated liquid and then grows to a frost crystal nucleus.