PURPOSE: To easily work a die for producing the die by taking such a constitution that an annular die for forming welding chambers different from and independent of both male and female dies is arranged between both dies.

CONSTITUTION: As for extruding hollow dies used for extruding a metallic hollow stock such as aluminum a die 4 for forming the welding chamber 11 different from and independent of both male and female dies 2, 3 is used and it is arranged between these male and female dies to form the welding chamber 11. consequently, difficult working of recessed parts for forming the welding chambers of the male die 3 and the female die 2 is eliminated and both male die 3 and female die 2 become easy to work. Since the die 4 for forming the welding chamber is of an annular structure, the manufacture, the working can be simplified. Further, since the die 4 for forming the welding chamber different from an independent of the male and female dies is adopted and fitting parts 5, 6 for centering are provided, the forming position for the fitting part for centering and its structure can be designed to the optimum.