PURPOSE: To remove strain of a cylindrical body caused by welding simply by welding small iron pieces on the weld line of a cylindrical body having a weld line in longitudinal direction.

CONSTITUTION: For instance, when a perforated type differential pressure Pitot tube is formed by welding bisected cylindrical bodies 1, 1' and a partition plate 2, bending due to welding strain occurs in the longitudinal direction of the plate 2 and deformation is caused. To straighten this, small iron pieces are welded on the weld line 3 of the cylindrical bodies at proper spacing. Then, arc is generated on the top of small iron pieces in a manner of spot welding using an electric welding rod, and the welding rod is molten and rapidly heated partially, and bent cylindrical body is straightened. When correction is completed, small iron pieces 7 are cut off by a saw etc.