PURPOSE: To automate a straightening work and to contrive to improve produc tivity by measuring a degree of the right angle for an H-shape before straightening, calculating an indentating value based on a deformation value of the H-shape and a spring back value, then straightening the degree of the right angle of the shape steel.

CONSTITUTION: Cylinders 15, 21 are moved and by elevating a supporting pin 14 guided by a guiding groove 18 of a frame 17, the position of the chock 13 is decided. Then, to make an inclination of a shaft 12 of indentating roller 11 to an angle of inclination corresponding to the spring back value, the cylinder 21 is actuated and the chock 13 is rotated centering around the supporting pin 14, then the setting of the roll 11 is finished. In this state, a cylinder 19 is actuated, the roll 11 indentates a flange through the frame 17, supporting pin 14, chock 13 by the intormation from a shape measuring device. In this state, the conveyance of the H-shape is advanced, the straighening of the degree of right angle is performed continuously while repeating the shape measurements of the H-shape.