An embedding hole is formed in a base made of thermoplastic resin, an embedded part is inserted in the embedding hole, the base is subjected to heating treatment for softening the base to bring the base into an elastomeric region and restraining treatment for restricting outward thermal expansion of the base to thereby expand the base in an inward direction of the embedding hole 2a to reduce a hole diameter and to deform a hole wall of the embedding hole along a shape of an outer wall face of the embedded part and to bring the hole wall into close contact with the outer wall face, and then the base is cooled and hardened.