PURPOSE: To fit an attachment while facilitating its positioning without requiring parts such as a calking pin, by forming through holes in a base material at specific positions, and extruding the attachment piece and a fastening part through the through holes on both sides of the base material.

CONSTITUTION: The base material 1 having the through holes 5 at the specific positions is held between a convex mold 7 and a concave mold 8 and then the tip part 9A of a resin injecting machine 9 is set in the injection hole 8C of the concave mold 6 to extrude molten synthetic resin. The injected resin is cooled and both molds 7 and 8 are removed to obtain a work 13 having the attachment 10 fixed to the base material 1. Namely, the base material 1 is formed while clampled with the fixture part 10A and fastening part 11, so the sticking tendency of the attachment piece 10 is excellent.