Provided is a means capable of improving the fatigue strength of an ear portion which is the fatigue high-risk portion of a torsion beam, causing minimal disadvantage in terms of productivity or costs. In particular, when shape-processing a tube (1) to be the torsion beam, a part of the tube (1) is crushed radially so as to have a nearly U-shaped cross section and thereafter bent with a bottom line (3) as the front side of bending, thereby imparting 2-6% pulling-side bending strain in the tube axis direction to the ear portion (2).