To provide a method for manufacturing an efficient filter medium.

A filter 15 is constituted so that stitches are formed by winding a strand 16 in multiple layers to form superimposed parts and the superimposed parts of the strand 16 of the specified adjacent layers being at least a part of the multiple layers are joined to each other by high-frequency induction heating. In the concrete, the filter 15 which is braided as a cylindrical body having the stitches formed by winding the strand 16 in the multiple layers is arranged in a heating coil 21, a high-frequency current is made to flow through the arranged coil 21 to generate an eddy current in the filter 15 and the superimposed parts of the strand 16 are joined to each other by heating the filter 15 by the eddy current loss.