PURPOSE: To improve working accuracy and to reduce cost by working the internal circumferential surface of a thick wall cylindrical stock to prescribed dimensions, then, fitting a jig in full surface contact into its internal circumferential surface under pressure to work the external circumferential surface and end face of the thick wall cylindrical stock.

CONSTITUTION: A solid shaft body 2 having a smoothly tapered external circumferential surface 2A is fitted smoothly into a thin wall sleeve body 4 and a thick wall cylindrical member 1 to be worked is arranged on its external circumferential surface 4B. A driving device 5 having a piston body 5A on the thick wall edge part 4E of the sleeve body 4 is provided between the sleeve body 4 and shaft body 2. Under this state, hydraulic pressure is supplied to oil supply holes 7, 8 of the shaft body 2 to push out the sleeve body 4 by a piston body 5A to the right. In this case, under the wedge action of a tapered surface forming an oil film, the sleeve body 4 holds a member 1 in strong internal pressure. Since high rigidity is obtained by integrating the shaft body 2 with the member 1, the working accuracy of the member 1 is improved. The reduction of working time reduces the cost.