PURPOSE: To eliminate troublesome operations for changing the holding of a brace by a method in which a worked model is fixed coaxially to the brace placed on a drive roller and two torches to cut off both ends of the brace are operated along the surface of the brace in the same form as the model.

CONSTITUTION: A horizontal pipe part of a brace 4 to make up the leg of an offshore working platform is placed on a drive roller 10, and the other end of a model shaft 12 having a model 11 on its one end is fixed to the inside of the brace 4 by a center 13. In working the end of the brace 4 into a desired shape, the brace 4 is turned by the drive roller 10 and the end of the brace 4 is cut off by the torch 21. In this case, the torch 21 at the tip of the torch base arm 17 is made to move along the surface of the brace 4 in the same shape as the model 11 on which a tracer 20 is pressed. The second torch base arm 17' is symmetrically moved by the induction of the model 11 through a rope 22. Both ends of the brace 4 can thus be concurrently cut off and worked to the shape of the model 11.