Torsion beam manufacturing method and torsion beam manufacturing apparatus

A torsion beam manufacturing method for manufacturing a torsion beam including a central portion of which a cross-section orthogonal to a longitudinal direction is a closed cross-section having a substantial V-shape or a substantial U-shape at any position in the longitudinal direction, and a shape changing portion which has a connection region leading to the central portion and including a closed cross-section having a shape different from the shape of the closed cross-section of the central portion, the method comprising:

• a preparation step of preparing a torsion beam material formed with the central portion and the shape changing portion;
• and
• a compression step of thickening at least the connection region through application of a compression force in the longitudinal direction to at least the connection region of the torsion beam material without applying a hydraulic pressure to an inside of the torsion beam material to obtain the torsion beam, after the preparation step.