To provide a bottom for a bed apparatus that can make the user feel comfortable when lying on the bed apparatus. The bottom for a bed apparatus, which is height adjustable and is mounted on the top of a bed apparatus, comprising a plurality of parts each formed of a resin plate having a thickness, including a back bottom, a hip bottom, a knee bottom and a foot bottom. Of the parts, essential parts are joined by connecting parts, and the connecting parts are formed of the same material with, to be thinner than, and integrally with, the essential parts, and, depressed portions are formed on the top surface of the bottom around the center in the width direction of the bottom, and a plurality of passage holes are perforated in the depressed portions from the top surface to the undersurface of the bottom.