Abstract: A fin-tube type heat exchanger having improved heat transfer rate is disclosed. The heat exchanger effectively restricts forming of separation bubbles on the back surfaces of the tubes fitted to the fin bodies, thus to promote smooth air flow in the heat exchanger and to improve heat transfer rate. The heat exchanger has the vertically placed fin bodies, the tubes horizontally penetrating the fin bodies, a plurality of dimples provided on opposed side surfaces of the fin bodies, and separation bubble controllers for reducing the size of separation bubbles formed about the tubes. The bubble controllers are provided on the opposed side surfaces of the fin bodies about the tubes. In another embodiment, the heat exchanger has no bubble controller but reduces the size of the separation bubbles by controlling configurations and directions of the dimples.