To improve convenience and comfortability by keeping a fixed interval so as not to separate a bottom corresponding to a back from the side of a head board in the case of raising a back.

When reclining a back bottom 34a through a lower frame member 39 by a back reising link 42, a roller 40 at the top end of lower frame member 39 moves a roller holder 41 on a movable frame 33, the movement of back bottom 34a facing a foot board 37 to the rising direction on the top end side is increased, the reclining action of back bottom 34a is promoted (reclining speed is accelerated), the back bottom 34a is reclined to a reclination angle (35°-40°), and the interval between the back bottom 34a and the head board 36 is kept equally with a case that the back bottom 34a is made flat.