To make installation always in optimum position using a clamp capable of retreating, compact the clamp device, reduce the costs, and establish the unmanned and power-saving operation.

A work clamp device 1 is composed of a work hold 5 to bear the undersurface of each work W, a clamp 7 to press the oversurface of the work W, and a clamp body 9 fitted with this clamp 7 and moves horizontally from the work pressing position to a retreat position apart from the work W. This work clamp device 1 can be installed in the optimum position at all times, and it is possible to compact the device and supress the costs.