A torsion beam type suspension comprising: a pair of left and right hollow trailing arms (1,2), each of the trailing arms (1,2) swingably supported at one end side of the trailing arm (1,2) by a vehicle body and rotatably supporting a vehicle wheel at the other end side of the trailing arm (1,2); a torsion beam connecting the pair of left and right trailing arms (1,2), the torsion beam having at both ends cutouts formed in correspondence to a cross-sectional shape of the trailing arms (1,2), each of the cutouts having an opening configured to receive a corresponding trailing arm of the trailing arms (1,2), the trailing arm (1,2) having a joining position to which the torsion beam is connected by welding and an inserting position where the trailing arm (1,2) is allowed to be inserted into the cutout through the opening, the opening being configured to be a size such that, when the torsion beam is located at the joining position, the torsion beam surrounds half or more of an outer periphery of the trailing arm (1,2) inserted into the cutout and the trailing arm (1,2) is not allowed to be inserted into the opening of the cutout from a radial direction of the trailing arm (1,2), characterised by the torsion beam type suspension further comprising upper-side and lower-side grooves (26, 28) and the opening being arranged such that, when the torsion beam is located at the inserting position, the trailing arm (1,2) is connectable to the torsion beam by inserting the trailing arm (1,2) through the opening of the cutout by moving the trailing arm relative to the torsion beam in a radial direction of the trailing arm (1,2), by aligning the upper-side and lower-side grooves and to the cutout, then moving the torsion beam relative to the trailing arm (1,2) along an axial direction of the trailing arm (1,2), and then welding at the joining position. a pair of left and right hollow trailing arms (1,2), each of the trailing arms (1,2) swingably supported at one end side of the trailing arm (1,2) by a vehicle body and rotatably supporting a vehicle wheel at the other end side of the trailing arm (1,2); a torsion beam connecting the pair of left and right trailing arms (1,2), the torsion beam having at both ends cutouts formed in correspondence to a cross-sectional shape of the trailing arms (1,2), each of the cutouts having an opening configured to receive a corresponding trailing arm of the trailing arms (1,2), the trailing arm (1,2) having a joining position to which the torsion beam is connected by welding and an inserting position where the trailing arm (1,2) is allowed to be inserted into the cutout through the opening, the opening being configured to be a size such that, when the torsion beam is located at the joining position, the torsion beam surrounds half or more of an outer periphery of the trailing arm (1,2) inserted into the cutout and the trailing arm (1,2) is not allowed to be inserted into the opening of the cutout from a radial direction of the trailing arm (1,2), characterised by the torsion beam type suspension further comprising upper-side and lower-side grooves (26, 28) and the opening being arranged such that, when the torsion beam is located at the inserting position, the trailing arm (1,2) is connectable to the torsion beam by inserting the trailing arm (1,2) through the opening of the cutout by moving the trailing arm relative to the torsion beam in a radial direction of the trailing arm (1,2), by aligning the upper-side and lower-side grooves and to the cutout, then moving the torsion beam relative to the trailing arm (1,2) along an axial direction of the trailing arm (1,2), and then welding at the joining position.