An electric bed includes a bed board unit, and an adjusting device mounted on a bottom of the bed board unit. The bed board unit includes a head board, a back board, a waist board, a hip board, a leg board and a foot board. The adjusting device includes a driving unit, a support unit, at least one track unit and at least one hinge unit. Thus, the waist board is pushed by the electric cylinder when the back board lies or is lifted, so that the waist board is operated independently and is lifted or lowered freely.