A method of sheet forming for manufacturing a sheet-formed part that is formed in an L-shape as viewed in a plan view and includes a top portion (21A, 21, 53), side wall portions (23, 55) formed on the respective both sides of the top portion (21A, 21, 53), and flange portions (25, 57) contiguously formed with the respective side wall portions (23, 55), by sheet-forming a metal sheet (11A, 11, 79A, 79) with the a sheet forming tool, the method comprising: a first sheet forming process in which the metal sheet (11A, 11, 79A, 79) is arranged on a first sheet forming tool including a first punch (3, 65), a first die (5A, 5, 69A, 69), a first blank holder (61, 7), and a pad (73, 9) so that a part corresponding to an end portion of a short side of the L-shape in the metal sheet (11A, 11, 79A, 79) does not overlap with the first die (5A, 5, 69A, 69) and the first blank holder (61, 7), a part of the top portion (21A, 21, 53) is held by the pad (73, 9), and the metal sheet (11A, 11, 79A, 79) is sheet-formed into a first sheet-formed part having an intermediate shape; and a second sheet forming process in which the first sheet-formed part formed in the first sheet forming process is sheet-formed into a second sheet-formed part having a top portion (21A, 21, 53) and a side wall portion (23, 55) whose shapes are identical with those of the sheet-formed part, with a second sheet forming tool having a second punch (15, 75) and a second die (17A, 17, 77A, 77), Characterised in that the side wall portion (23, 55) on an outer side that includes an L-shaped bent portion in the first sheet-formed part formed in the first sheet forming process is outwardly stretched in an arcuate shape as viewed in a plan view front the side wall portion (23, 55) of the sheet-formed part, a curvature radius of a circular arc of the side wall portion (23, 55) stretched in an arcuate shape is larger than a curvature radius of the L-shaped bent portion of the sheet-formed part, an outside of the top portion (21A, 21, 53) of the L-shaped bent portion is stretched from an outside of the top portion (21A, 21, 53) of the sheet-formed part, and a curvature radius in a cross section of a shoulder portion contiguously formed with the top portion (21A, 21, 53) stretched, as viewed in a side view, is larger than a curvature radius in a cross section of a shoulder portion contiguously formed with the outside of the top portion (21A, 21, 53) of the L-shaped bent portion of the sheet-formed part, as viewed in a side view. a first sheet forming process in which the metal sheet (11A, 11, 79A, 79) is arranged on a first sheet forming tool including a first punch (3, 65), a first die (5A, 5, 69A, 69), a first blank holder (61, 7), and a pad (73, 9) so that a part corresponding to an end portion of a short side of the L-shape in the metal sheet (11A, 11, 79A, 79) does not overlap with the first die (5A, 5, 69A, 69) and the first blank holder (61, 7), a part of the top portion (21A, 21, 53) is held by the pad (73, 9), and the metal sheet (11A, 11, 79A, 79) is sheet-formed into a first sheet-formed part having an intermediate shape; and a second sheet forming process in which the first sheet-formed part formed in the first sheet forming process is sheet-formed into a second sheet-formed part having a top portion (21A, 21, 53) and a side wall portion (23, 55) whose shapes are identical with those of the sheet-formed part, with a second sheet forming tool having a second punch (15, 75) and a second die (17A, 17, 77A, 77), Characterised in that the side wall portion (23, 55) on an outer side that includes an L-shaped bent portion in the first sheet-formed part formed in the first sheet forming process is outwardly stretched in an arcuate shape as viewed in a plan view front the side wall portion (23, 55) of the sheet-formed part, a curvature radius of a circular arc of the side wall portion (23, 55) stretched in an arcuate shape is larger than a curvature radius of the L-shaped bent portion of the sheet-formed part, an outside of the top portion (21A, 21, 53) of the L-shaped bent portion is stretched from an outside of the top portion (21A, 21, 53) of the sheet-formed part, and a curvature radius in a cross section of a shoulder portion contiguously formed with the top portion (21A, 21, 53) stretched, as viewed in a side view, is larger than a curvature radius in a cross section of a shoulder portion contiguously formed with the outside of the top portion (21A, 21, 53) of the L-shaped bent portion of the sheet-formed part, as viewed in a side view.