PURPOSE: To permit a workpiece to be automatically secured by allowing the piston rods of the internal operation cylinders for supplying working fluid for the securing cylinders to be operated from outside.

CONSTITUTION: A jig body 1 equipped with a lifter 3 on which the workpiece is mounted, is provided with locator cylinders 26 and 38 and a clamp cylinder 40 operated by air pressure or fluid pressure such as oil pressure to secure the workpiece to the bed, and internal operation cylinder 14 and 15 having piston rods 16 and 17 operated from outside to control the securing action and the removal of the action of said securing cylinders 26, 38 and 40 by supplying the compressed fluid for them. Consequently, this permits the workpiece to be automatically secured or removed, and eliminates the need for the installation of the supply pipe of air pressure or the like to operate the securing cylinders between the jig body 1 and the fluid pressure source.