PURPOSE: To rapidly and easily carry out straightening work of the title shape steels by supporting shape steels by a shape steel holding body via plural arresting tools and welding these and subsequently, straightening thermal deformation generated at the time of welding by the plural straightening tools.

CONSTITUTION: The shape steel holding body 1 consisting of circular connecting plates 5A and 5B to connect ends of a couple of upper and lower beams 4A and 4B to each other is supported freely rotatably round the horizontal axial center by a couple of supporting rollers 6 on right and left. The plural arresting tools 13 to arrest the shape steels are then provided to the one beam 4A and the plural straightening tools 14 to straight the shape steels are provided to the other beam 4B. Moving bodies to approach and separate from the shape steel holding body 1 are then arranged respectively to the right and left of the shape steel holding body 1 and traveling bodies to travel along the beams 4A and 4B of the shape steel holding body 1 are provided respectively to the respective moving bodies and welding tools to weld shape steels in a tack-welded state are set respectively to said traveling bodies. Accordingly, the straightening work can be rapidly carried out as compared with the case where straightening is carried out by using a press machine separately.