To prevent a clamping mark on the front surface side and to prevent a flaw even if an external wall material such as a siding material is clamped.

A clamp device is provided with a reference surface table 1 having the reference surface 10 on which a body to be clamped P is to be placed, and a clamp plate-shaped body 2 to be moved in relation to the reference surface table 1 and for clamping the body to be clamped P placed on the reference surface between it and the reference surface table 1. The reference surface 10 of the reference surface table 1 is partially cut to form a cutout part 10a, and a rising and lowering presser 100 having an irregular surface 100a is provided on the cutout part 10a so as to be freely raised and lowered. The rising and lowering presser 100 presses one surface of the body to be clamped P by the irregular surface 100a from the opposite direction to a direction in which the clamp plate-shaped body 2 is moved to the reference surface 10, a soft body 20 is provided on the contact surface 20a of the body to be clamped in the clamp plate-shaped body 2, and the other surface of the body to be clamped P is pressed by the soft body 20, and the body to be clamped P is clamped.