PURPOSE: To obtain the effect of boundary layer control by forming the vane part of a fan with a porous material of metal, synthetic resin, or ceramic, etc.

CONSTITUTION: The vane 1 of a sirocco fan is formed with a porous material of synthetic resin, metal or ceramic, etc. As shown by the cross section 4 of the vane 1, numerous pores are formed passing through the vane 1 from the bottom end to the top end, leading part of air flow on the bottom face side of the vane to the top face, to accelerate the relatively low velocity of air flow of a boundary layer on the surface. And, due to the effect of air flow 5, more uniform distribution as shown by the velocity distribution 7 can be obtained, preventing separation from a vane surface and reducing noise caused by the turbulence of air flow.