PURPOSE: To obtain a molded piece free from cracking by using polyamide-imide resin with a specified soluble viscosity in compression molding of thermoplastic polyamide-imide resin.

CONSTITUTION: Polyamide-imide resin is heat-treated. The heat-treatment changes the polyamide-imide resin having the maximum soluble viscosity 2×105 poises at 340°C into the polyamide-imide resin having the minimum viscosity 3×105 poises under heating atmosphere. In this compression molding, the heated mold is filled with polyamide-imide resin powder that does not absorb water and has been heattreated and then, pressure is given to the powder as heated at the melting point min. After pressure is given, the mold is cooled and a molded piece is taken out of the mold. The molded piece obtained is postcured. Accordingly, though the mold is cooled after compression molding the molded piece is free from cracking. While the molded piece is taken out of the molded no cracking occurs. Additionally, in the post cure process cracking is prevented from occurrence.