<；P>；PROBLEM TO BE SOLVED: To provide a sitting position changeable chair device which corresponds to both of a tilting function and a reclining function by a simple structure. <；P>；SOLUTION: This chair device 3 is constituted of a seat back frame 17 and a reclining actuator 19. In this case, the seat back frame 17 constitutes a seat under frame 16 on which a sitting seat 5 is mounted, and a backrest section 6. The reclining actuator 19 drives a mount frame 15 which integrally supports the seat back frame 17, and a reclining mechanism 21. The seat back frame 17 is longitudinally and tiltably supported by the reclining actuator 19. The rear end section of the seat under frame 16 is pivoted by either one of the rear section of the mount frame 15 or the lower section of the seat back frame 17, and the chair device is formed to be freely vertically rockable. At the same time, a switching means 31B which can selectively switch the seat back frame 17 and the seat under frame 16 between a reclining position where a relative tilting angle between them can be changed, and a tilting position where the tilting angle between them is fixed at a specified angle is provided. <；P>；COPYRIGHT: (C)2007,JPO&INPIT
