A clamping device increases the diameter of a gripping assembly that is inserted into a hole in a workpiece and thus grips the inner circumferential surface of the hole, and particularly relates to such a clamping device that is adapted so that, in the vicinity of a scraper, no clearance occurs between the gripping assembly and a clamp rod, and the scraper. The clamping device is capable of enhancing the durability of a scraper, reducing the amount of pressurized air consumed by blowing, and ensuring the strength of a clamp rod against pulling and so on.