A method and apparatus for making axial-flow filters wherein a sectorial-shaped sheet of filter material having corrugations therein parallel to the curved ends thereof is made from a flat sheet of filter material in the first step, and thereafter the corrugated sheet is made into an annulus to obtain the final product. In the first step, an edge portion of a flat sheet of filter material is attached to a sectorial-shaped mold, having a mold surface defined by curved ridges and valleys parallel to the curved ends of the mold, so that the sheet is slanted up away from the mold surface from the smaller curved end of the mold. Thereafter a set of curved forming blades is moved down toward the mold to engage the sheet and to fold it successively and consecutively across the ridges of the mold and beneath the edges of the blades into the valleys of the mold to corrugate the sheet. In the second step, the corrugated sheet thus produced is made into an annulus by using a contouring belt which embraces the larger convexly curved ends of the sheet and constricts the sheet into an annulus.