A method for manufacturing a vehicle body member in which a second sheet material is placed on and joined to a first sheet material and a joined sheet material formed by the joining of the first and second sheet -materials (120, 130) is press formed into a vehicle body member with a predetermined shape, characterized by comprising: a joining step of joining the second sheet material to the first sheet material by welding at a plurality of points including a first joint and a second joint which are separated from each other, thereby forming the joined sheet material; a forming step of press forming the joined sheet material so that a ridge (R1, R2) crossing an imaginary line segment connecting the first joint and the second joint is formed in a portion where the first sheet material overlaps the second sheet material; a preparation step of, before the joining step, forming a displacement facilitating portion (34, 36), which facilitates displacement of the second sheet material relative to the first sheet material in a longitudinal direction of the imaginary line segment, in a portion corresponding to between the first joint and the second joint in the second sheet material, characterized in that, the first sheet material is an elongated member extending in a predetermined direction, in the forming step, the joined sheet material is formed so as to form two of the ridges (R1, R2) extending in a longitudinal direction of the first sheet material on both sides of the displacement facilitating portion (34, 36) and a wall connecting the two ridges (R1, R2), in the preparation step, the displacement facilitating portion (34, 36) is formed in a portion corresponding to the wall in the second sheet material, the displacement facilitating portion (34, 36) includes a slot extending in the longitudinal direction of the first sheet material, in the preparation step, a plurality of the slots that are located next to each other at intervals in the longitudinal direction of the first sheet material are formed in the second sheet material, and in the joining step, the second sheet material is welded to the first sheet material at a third joint located between adjacent ones of the slots. a joining step of joining the second sheet material to the first sheet material by welding at a plurality of points including a first joint and a second joint which are separated from each other, thereby forming the joined sheet material; a forming step of press forming the joined sheet material so that a ridge (R1, R2) crossing an imaginary line segment connecting the first joint and the second joint is formed in a portion where the first sheet material overlaps the second sheet material; a preparation step of, before the joining step, forming a displacement facilitating portion (34, 36), which facilitates displacement of the second sheet material relative to the first sheet material in a longitudinal direction of the imaginary line segment, in a portion corresponding to between the first joint and the second joint in the second sheet material, the first sheet material is an elongated member extending in a predetermined direction, in the forming step, the joined sheet material is formed so as to form two of the ridges (R1, R2) extending in a longitudinal direction of the first sheet material on both sides of the displacement facilitating portion (34, 36) and a wall connecting the two ridges (R1, R2), in the preparation step, the displacement facilitating portion (34, 36) is formed in a portion corresponding to the wall in the second sheet material, the displacement facilitating portion (34, 36) includes a slot extending in the longitudinal direction of the first sheet material, in the preparation step, a plurality of the slots that are located next to each other at intervals in the longitudinal direction of the first sheet material are formed in the second sheet material, and in the joining step, the second sheet material is welded to the first sheet material at a third joint located between adjacent ones of the slots.