PURPOSE: Projections formed every time when a nozzle for passing through a polymer is punched on a thin plate for a spinneret with a punching tool are absorbed by a spongy thin plate to prevent the uneveness in the depth of the polymer-introducing holes and the deformation of the nozzles during the punching of many nozzles.

CONSTITUTION: A spongy or mesh plate 10 is laid between the plate 3 for spinneret and the base 2' with a flat surface and the plate 3 fixed to the base, then punching is effect by use of a puncing tool 4. The projections 8 formed by punching preliminary holes 5a are absorbed by the thin plate 10. The projections 8 on the bottom surface is flatened by grinding and a new spongy or mesh plate 10 is placed and the second punching is effected with the puncing tool 4 to finish the polymer- introducing holes 5. Then, the projections 8' are removed by grinding and another punching tool is used to form throhgh-holes for yarn nozzles.