PURPOSE: To reduce weight without using metal for core materials by a method wherein connecting sections and wire fixing sections are formed at locations adjacent to an outer fringe of a hollow molding used as a seat back for an automobile, a trimming wire is mounted to the wire fixing sections and a cover is fitted to the connecting sections.

CONSTITUTION: A plurality of connecting sections 6 and wire fixing sections 7 which hold the connecting sections and are formed in projecting shapes are made up at locations adjacent to an outer fringe of a hollow molding 1. On the other hand, a trimming wire 10 is built up which is mounted crossing the wire fixing sections 7 and is used for connecting the end sections of a cover member 3, the trimming wire 10 is placed at the wire fixing sections 7, the wire fixing sections 7 are heated and deformed to fasten the trimming wire 10 to the hollow molding, and the end sections of the cover member 3 are connected to the connecting sections 6. Thus, since a metal material is not used as core materials, weight is reduced, and the cover member 3 can simply be fitted rapidly.