To provide an inexpensive air filter increased in its collecting area and enhanced in dust removing effect.

A large number of projections 4 are provided to the plane 3 of a filter main body 1 which has vent holes provided thereto in a lattice-like pattern so as to be raised therefrom in a rod-shaped or fluffy state and deformed by secondary processing. Since the secondary processing of these projections is performed by heating processing or pressing processing, the deformation of the projections can be certainly performed and secondary processing can be simply performed in low cost.