In a twin-screw extruder including a barrel, which has two screws disposed in parallel in its inside and an opening at one edge, and an extrusion molding die disposed to the opening side of the barrel through a straightening vane and a filter net, the straightening vane includes a first straightening vane and a second straightening vane, the first one has a hole forming region having plural through holes formed in a region whose size and shape are in agreement with the size and the shape of the inner periphery of the opening portion, and the second one has a hole structure whose size and shape of its inner periphery at one opening edge are in agreement with the size and the shape of the hole forming region, and its sectional area is reduced once in a process to the other opening edge and then expanded in a taper shape.