PURPOSE: To continuously manufacture a porcelain insulator a short time as a product which is the same as the ordinary product in quality by extruding specified ash soil from a tug mill and immediately performing the soil through a round trowel forming process and successively carrying out finish forming for a final shape.

CONSTITUTION: A cake 1 containing moisture at 17-19% is put in a vacuum tug mill 2 to be kneaded while it is vacuum-deaired, so that it is pushed as ash soil 3 containing extremely low moisture at 17-19%. Next, this ash soil 3 is cut in a prescribed length by a cutter 4, and immediately transferred to the inside of the mold 9 of a preforming machine 8 by means of an ash soil transshipment machine 7 to be preformed by pressing with a round trawel which rotates the ash soil 3 in the mold 9. Thereafter, the preformed product is transferred to a finish forming machine 15 by a reversal transshipment machine 14 and placed on the setter 18 of a finish forming machine 15 to be cut for finish forming in a final shape by a bite 21. It is thereby possible to continuously complete the manufacturing process of a porcelain insulator from extrusion of ash soil to finish forming a short time so that the porcelain insulator which can stand comparison with the previous ones in quality can be obtained.