To prevent carbide from forming and accumulating and enable a flow path for filtering molten resin to sustain for extrusion operation for a long time when PVDC resin is extrusion-processed by prevent a holding member for holding the inner wall part forming an annular resin flow path from being substantially brought into contact with a filter.

As an annular flow path for a filter, the flow path is formed by a part for holding the filter and a part for holding a central member 2 forms a cylindrical column resin flow path and e.g. a part wherein 8 pieces thereof are equally arranged is used. In addition, supporting legs 8 as holding members existing among them have respectively a cut 7 with 90 degrees on the side where the filter is fixed so as to avoid bringing into contact with the filter part and to suppress retention at the end part of the supporting leg, both end parts is pref. at an acute angle. The central member is mode to be approximately symmetric conical projections 5 and 6 on its upstream side and downstream sides and has a structure fixing the central region of the filter at the part.