PURPOSE: To make it possible to manufacture a stable and high-quality molding excellent in properties of mixing with coloring agent or assistant with lower manpower and less costs, by forming a recessed part in the surface of an uncolored thermoplastic resin pellet, wherein the depth of said recessed part is larger than the width of said surface, mixing this pellet with powder coloring agent and agitating this mixture, forcing the coloring agent into said recessed part and then heating to fuse this pellet.

CONSTITUTION: In a pellet 1 in which a plurality of grooves 2 is formed in the axial direction, the groove 2 in the surface of said pellet is formed so that the depth of said recessed part is larger than the width of the opening, and said groove intrudes into the inside of said pellet 1. This pellet 1 is made by a type of extrusion molding process, where a thermoplastic resin for pellet forming is kneaded in a kneader-extruder and extruded, and extruded material is cut by a cutter to a predetermined length. Therefore, if said resin is mixed with powder coloring agent and agitated, due to its large surface area the contact ratio of coloring agent and/or assistant is increased and also the diffusion and mixing properties are improved, so that a stable molding of uniform quality can be manufactured.