Fins such as corrugated fins or plate fins are formed with meandering projections. A fluid such as air strikes bent parts of the meandering projections or grooves at the back sides while flowing along the fins and becomes turbulent and therefore flows while meandering so as to be directed toward the surfaces of tubes, so flows not only contacting the front and back surfaces of the fins without leaving any dead space, but also striking the surfaces of the tubes. Due to this, no boundary layers are formed at the surfaces of the fins or tubes, so heat conduction is promoted and therefore the heat exchange efficiency between a first fluid such as a refrigerant flowing through the insides of the tubes and a second fluid such as air flowing outside is remarkably improved.