In the present invention, in accordance with a tilt and back-raising command (Step S1—；Yes), knee-raising operation for raising the knees of the user is performed by actuating a knee bottom placed on a top frame (Step S2). Next, after execution of the knee-raising operation, tilting operation for making the head-side height of the top frame higher than the foot-side height of the top frame by moving up and down the head side and foot side of the top frame relative to the floor (Step S3). By this, the user can take a comfortable position just like sitting in the final position after the user's back has been raised, and it is possible to reduce user's feeling of being pressed on the back and in the belly and prevent user's significant body slippage.
