PURPOSE: To hold a member to be worked in an extremely short time and to easily change holding force to a desired value by coupling a pressure chamber and working chamber detachably from each other and freely releasably holding the peripheral edges of the member to be worked.

CONSTITUTION: The working chamber 13 is first spaced from the pressure chamber 12 and the member P to be worked is disposed in a prescribed position within the working chamber 13 in the space generated by this spacing. The working chamber 13 is then coupled to the pressure chamber 12 and thereafter, the peripheral edges of the member P to be worked are held by holding means 31, 33, 34. The member P is worked by the impact pressure in the pressure chamber 12 by detonation. The driving power for generating the driving power for generating the holding power of the holding means 31, 33, 34 is regulated by properly changing the fluid pressure when, for example, fluid pressure cylinders 33 are adopted for the holding means when the working conditions are changed. Then, the rapid setting of the member to be worked according to the cycle of detonation generation is possible and the productivity thereof is improved.