To suppress a sudden decline in the amount of heat exchange at the time of frosting, and to decrease the frequency and time of defrosting operation, concerning a heat exchanger with a fin, which receives and transmits heat between the refrigerant and air of air conditioners, refrigerating machines, car equipment, etc., and fluid such as air.

A heat insulating cut 7 is provided between a heat transfer tube 2 and a louvered part 6 in the direction in which the heat conducting path between the heat transfer tube 2 and the louvered part 6 is lengthened. Thereby, the heat conduction to the louvered part 6' adjoining the heat transfer tube 2 with the large amount of frosting is suppressed, and the frosting to the louvered part 6' adjoining the heat transfer tube 2 is eased. The sudden decline in the amount of heat exchange at the time of heating operation can be suppressed, and also the time of heating operation can be extended by allowing relatively uniform frosting.