A clamping device includes a cylinder, a base body, a movable plate, and holding pins. The movable plate is attached to the base body substantially parallel thereto via two pairs of link arms. The movable plate moves along the operating direction of the cylinder. The movable plate can abut against a width-direction side surface of a workpiece. The holding pins are attached to the movable plate. The holding pins abut against an upper portion of the workpiece.