PURPOSE: To prevent the back flow to the upper stream side of a flow passed through a fan and enhance the efficiency of the fan by integrally mounting a centrifugal component element turned nearly in parallel to a plane including the axial line of the fan on the side surface of a fan blade.

CONSTITUTION: An axial-flow fan 10 has eight fan blades 12 integrally mounted around a plastic boss part 11. In this case, the body part 13 of each fan blade 12 is formed into the same twisted form as a general fan, but a nearly triangular auxiliary member 14 and a centrifugal component element 15 are integrally connected to about its top. Namely, the centrifugal component element 15 is formed nearly into a triangle having one side connected to one side of the auxiliary member 14. The radial top part of the centrifugal component element 15 is disposed in the same radial directional position as the top of the body part 13 of the fan blade, and the outer diameter size of the fan is held as it is. Thus, a back flow in which the flow passed through the fan is turned around to the front side of the fan is prevented, and the flow rate of the fan is increased to enhance the fan efficiency.