PURPOSE: To stably produce a porous hollow filament by mixing and compressing a liq. org. polymer at the mixing and compressing part of an extruder, sending the liq. to the discharge part, and discharging the liq. from the discharge part.

CONSTITUTION: A powdery org. polymer and a liq. additive are separately s applied to the feed part of a two-shaft screw extruder means. The org. polymer and liq. additive are mixed at the mixing part of the extruder means to prepare a substantially liq. material. The material is then further mixed and compressed at the mixing and compressing part of the extruder means, sent to the discharge part, and discharged from the discharge part to produce a porous molded product. More than 30 pts.wt. of the additive is appropriately mixed with 100 pts.wt. of the org. polymer.