To provide a bottom for a bed apparatus that can relieve the sensation of being pressed and that at the same time is lightweight, easy to transport and can be cleaned easily. A bottom for a bed apparatus having a back-raising mechanism, includes a flexing bottom that is arranged between a back bottom and a hip bottom and can be flexed. In a back-raising operation, the flexing bottom flexes between the back bottom and the hip bottom while sliding downward over the surface of the uprising back bottom.
