To enable the extrusion of a hollow material having good size and shape precisions by holding a core in a die member for holding in the mode that the core is restricted to move in the front and rear direction.

The core 6 is restricted to move in the rear side by a come-off preventing action with a supporting piece 9 passed through a supporting hole part arranged in a bridge part 14 and a supporting hole part 11 arranged in the core 6. Then, it is prevented that the core 6 is moved to the rear side in the core inserting hole of te bridge part 14. By this constitution, the discrepancy of relative positional relation in the front and rear direction between a hollow part forming bearing part 4 in the core 6 and a forming hole bearing part 3 in a female die 2 is not caused and the hollow material E having good size and shape precisions is extruded.