A hospital bed includes a carrier frame, a driven wheel unit disposed below the frame, a motor unit, a drive wheel unit disposed below the frame and coupled operably to the motor unit in such a manner that actuation of the motor unit results in rotation of the drive wheel unit. A lifting-and-lowering device interconnects the frame and the drive wheel unit for lowering and lifting the drive wheel unit with respect to the driven wheel unit between an upper position, in which, the drive wheel unit is disposed at an elevation above the driven wheel unit, and a lower position, in which lower surfaces of the driven and drive wheel units are flush with each other.