A torsion beam type suspension device is provided in which a trailing arm part and a torsion beam part are formed as a unit by press-forming a tailored blank material in which end parts of plate materials having different thicknesses are butt-welded via a weld part. A weld part of the tailored blank material comprises a U-shaped cross section in which front and rear side wall portions are connected via a bottom wall portion, and a pair of cutouts are formed at the edge of each of the side wall portions at positions sandwiching the weld part, and therefore, when the torsion beam part is twistedly deformed, shifting the concentration of stress from the weld part to the cutout enables peeling apart of the weld end part to be prevented and the durability of the torsion beam type suspension device to be enhanced.