A die with a negative clearance where the length or the diameter of a punch (2) is set greater than that of a die (3) is used to form a dowel section by press working. The dowel section is needed as a guide for a tongue inserted into a buckle and as a load receiver when a latch member is elongated in a collision etc. The dowel section is formed at portions that are to be side walls at both sides of a buckle base member. When a ratio C/t that is the ratio of a clearance C to the plate thickness t of the buckle base member is from -30% to -5%, no cracks occur in the root of the dowel section, and the dowel section of a shear cross-section length is more than 0.25*t, a shear cross-section starting height is more than 0.7*t, and height is (0.70-0.95)*t is easily obtained, and the perpenducularity of the side faces of the dowel section is improved.