A work-clamping unit includes a base plate in which hydraulic cylinders are totally embedded, each cylinder including a piston vertically movable beneath the top surface of the base plate, the piston being adapted to carry a clamping member detachably connected thereto so as to transmit a clamping force from the piston to the clamping member, the base plate additionally including an oil path for feeding hydraulic pressure to each of the cylinders.