To obtain the subject KONJAK (paste made from the starch of devil's tongue) having uniform thickness with a simple process in high efficiency at a low cost by extruding a paste containing glucomannan and a coagulant with a specific extrusion tool.

A pasty material is produced by stirring glucomannan, a coagulant and optional arbitrary subsidiary raw material with water of an amount not to cause the complete swelling of the glucomannan. The pasty material is supplied into an extrusion tool 1 with pressure and extruded from the upper inlet port 3 to the lower outlet port 4 of an extrusion groove 2 formed in the extrusion tool 1. The extrusion tool 1 is composed of a feeding port 5 for the pasty material, a paste-holding part 6 and an extrusion groove 2 having the inlet port 3 and the outlet port 4. The extrusion pressure applied to the paste in the course of passing through the groove 2 is distributed and uniformized in the lateral direction of the groove 2 by adjusting the distance between the inlet port 3 and the outlet port 4.