PURPOSE: To manufacture a large forging forming vessel by a small-sized forging device by extruding a stock to a free extension space from an extruding gap between the peripheral edge of an opening part of a holding die, and a control die.

CONSTITUTION: A stock M is put into a stock holding part 7 of a stock holding die 3. Subsequently, a control die 4 is placed in a prescribed position, and pressure is applied to the stock M by a pressing rod 5. The stock M is extruded in the peripheral direction from an extruding gap (d). As for the stock M, its extension stops in the place separated by a prescribed distance or above from the extruding gap (d), and a cylindrical body 10 of a large diameter size is formed. The cylindrical body 10 is not guided to the constitution face of both of the holding die 3 and the control die 4, and the diameter size of the cylindrical body 10 is determined by an extension caused by a first extrusion of the stock M from the extruding gap (d). In such a way, a large forging forming vessel can be manufactured by a small-sized forging device.