PURPOSE: To obtain fine powder good in fluidity, to raise the rotating speed of a grinding edge and also to reduce abrasion and to enhance production efficiency by leaps and bounds by performing ceramic coating having prescribed thickness in the mutually opposite edge parts in a grinding male edge and a grinding female edge which are relatively rotated.

CONSTITUTION: Both a grinding male edge 4 and a grinding female edge 5 are constituted so that these edges are mutually rotated in the reverse direction. The relative speed of the mutually opposite edge parts 3a, 3b is particularly raised. Furthermore, hardness is raised by leaps and bounds by performing ceramic coating 19 having prescribed thickness in the opposite edge parts 3a, 3b. Abrasion is drastically reduced. Fine powdery synthetic resin which is good in fluidity and has constant quality is continuously produced in a range over a long period. Further, since the relatively rotating speed of both grinding edges 4, 5 is high, grinding velocity is raised. Grinding amount per unit time is drastically increased and production efficiency is enhanced by leaps and bounds.