An electric bed comprises an adjusting device on the bottom of a bed board unit which comprises at least a back board 21, a waist board 22 and a hip board 23 and a frame. The adjusting device comprises a driving unit (10, fig. 1) which has an electric cylinder (100, fig. 8) and a drive rod (101, fig.8) and is secured to the bottom of the hip board 23. A first support bar (110, fig. 3) is mounted on the waist board 22 and a second support bar (111, fig.3) is mounted on the hip board 23, and the bars are connected together by a first hinge (130, fig.3). The first support bar is connected to the drive rod 101. A track unit is provided, comprising a slideway (120, fig.4) mounted on the frame and a slide (121, fig.4) mounted on the back board 21. At least a first hinge (131, fig.6) is connected between the back board 21 and the waist board 22. Thus, the waist board can be operated independently.
