PURPOSE: To manufacture a square tapered tube of large diameter by pressing, compressing the central axis of a round steel tube from its outside.

CONSTITUTION: When the diameter of a square tapered tube is given by 1.00, the recessed part of a truncated cone having nearly a 1.27 diameter is formed by an upper die 1 and a lower die 2. The recessed and projecting surfaces are engaged with each other on the mating faces of the upper and lower dies, the side surface of a member to be worked in the recessed part 3 of the truncated cone is always born by a guiding part 4 and holds a longitudinal thrust in a drawing time. The truncated cone is pressed by the upper and lower dies 5, 6 having the recessed part of a truncated pyramid having really the same constitution into the truncated pyramid at the following stage. This plan requires no core die and no die change by change of the plate thickness of the material, etc.