A plurality of heat transfer tubes are disposed at certain intervals, in-tube operating fluid (such as coolant) passes therethrough, and a plurality of small-gage wires are used as a heating fin. One small-gage wire is wound at a pair of heat transfer tubes 1a and 1c in a spiral manner, and another small-gage wire is wound at a pair of heat transfer tubes 1b and 1c in the spiral manner, and still another small-gage wire is wound at a pair of heat transfer tubes 1b and 1d in the spiral manner. Thereby, while higher heat transfer coefficient can be achieved, and a heating surface area is ensured, clogging can be avoided even when moisture in air condenses on a surface of a heat exchanger. As a result, it is possible to realize a high-performance and compact heat exchanger used for air conditioning.