To prevent the permanent set of backup members and damage by a plastic flow to the side of the inside face of a die even a press device is used under high pressure.

This device is an isotropic pressure press device in which a forming die 4 consisting of an elastic body is arranged in the inside of the die 3 and the compressive force in the axial direction of punches 5, 6 which are inserted into the die 3 is converted into the approximately isotropic compressive force by acting on the forming die 4 and which is provided with ring-shaped elastic backup members 10 between the punches 5, 6 and the forming die 4. Slopes 12 which face to the outward direction of a diameter and act so as to expand the backup members 10 in the outward direction of the diameter are formed in the edge parts of the punches 5, 6 which are opposed to the forming die 4.