A filter used for air cleaners. In this filter, a filter medium, which is obtained by folding a piece of elongated filter paper so that ridges and valleys are formed alternately, fitting spacers on this folded filter paper so as to maintain the spaces among the ridges and valleys properly, and then bending the resultant product so that the ridges and valleys extend in the radial direction, is set in a filter body having air inlet and outlet ports. A cushion material is inserted between the contact portions of the filter body and filter medium.