A vehicle seat is provided comprising a seat back frame having right and left side frames, a headrest for supporting a head of a seat occupant, and a back-and-forth movable body provided inside a backrest that is positioned at a rear of the seat occupant, wherein a backward movement of the back-and-forth movable body forwardly moves the headrest to support the head of the seat occupant. The filter receives a high and very low frequency static pressure attendant with a high frequency low dynamic pressure at one end, the filter operates to filter said high frequency dynamic pressure to provide only the static pressure at the other filter end. The first contact region of the transmission element may be arranged such that it is penetrated by the first force action axis. A viscosity of the composition at 100\xb0 C. By making the deposition pressure not lower than 800 Torr, the crystallinity of the III-V Group nitride compound semiconductor can be markedly improved and its defect density reduced. It is also suitable as a part of a vault, and as a complex shell consisting of a single continuous surface for exhibition or station buildings.