To provide a structure improved for a head rest and a side frame because the lack in each strength of the head rest and the side frame in an emergency is really found although various measures are taken because whiplash injury and the other injury of disease or the like are caused since the head cannot protected by the head rest and the upper body cannot be protected by the side frame in a supporting structure of a bracket provided in a conventional upper frame.

In the supporting structure of a headrest bracket, mounting wall pieces are formed on both ends in the longitudinal direction of a mounting part of an upper frame. Then, in the mounting part, one projection piece of a clinch side surface of a bracket, and an upper end and a lower end of the mounting part are welded. Also, the mounting wall piece on a free end side, and the other projection piece of the bracket are welded.