FIG. 1 and FIG. 2 are a perspective view and an elevation view, respectively, of a vehicle seat equipped with an occupant restraint apparatus according to an embodiment of the present invention, FIG. 3 is a view along arrows III-III of FIG. 2, FIG. 4 is a cross-section view taken along lines IV-IV of FIG. 5, FIG. 5 and FIGS. 6 a and 6 b are cross-section views taken along lines V-V and lines VI-VI