A method for reducing a springback that occurs in a part formed by press forming a metal sheet, the method comprising: an analytic model forming computer-implemented step of forming an analytic model of the press-formed part with plane elements and/or solid elements; a stressed-state setting computer-implemented step of setting each of the elements of the analytic model to a stressed state that causes the springback; a rigidity-contributable-portion detecting computer-implemented step of performing a topology optimization analysis on the analytic model with the elements set in the stressed state to detect a portion of the press-formed part that highly contributes to the rigidity thereof; the topology optimization analysis including analyzing the analytic model of the press-formed part to leave the minimum elements that most highly contribute to the rigidity under specific load constraint and volume percentage conditions, a computer-implemented step of subjecting the analytic model to an analysis of reverse press forming back to a flat sheet, thus finding a rigidity contributable portion (71a, 41a) in a blank sheet corresponding to the rigidity contributable portion (71a, 41a) of the analytic model, a rigidity improving step of applying a rigidity improvement to the contributable portion (41a, 71a) of the blank sheet (41, 71) on a basis of the portion detected by the rigidity-contributable-portion detecting step, wherein the rigidity improving step performs one or more of increasing a thickness of the rigidity contributable portion (41a, 71a) of the blank sheet (41, 71) by blanking the rigidity contributable portion of the blank sheet and joining a sheet member formed from a thicker sheet and having the same shape as the rigidity contributable portion of the blank sheet, thus forming a tailored blank sheet, increasing a Young's modulus of the rigidity contributable portion of the blank sheet by blanking the rigidity contributable portion of the blank sheet and joining a sheet member having a higher Young's modulus and having the same shape as the rigidity contributable portion of the blank sheet, thus forming a tailored blank sheet, and bonding another sheet to the rigidity contributable portion of the blank sheet for reinforcement by welding or bonding with adhesive a sheet member of another sheet material formed into the same shape as the rigidity contributable portion of the blank sheet, thus forming a reinforced blank sheet, and a step of press-forming the tailored or reinforced blank sheet. an analytic model forming computer-implemented step of forming an analytic model of the press-formed part with plane elements and/or solid elements; a stressed-state setting computer-implemented step of setting each of the elements of the analytic model to a stressed state that causes the springback; a rigidity-contributable-portion detecting computer-implemented step of performing a topology optimization analysis on the analytic model with the elements set in the stressed state to detect a portion of the press-formed part that highly contributes to the rigidity thereof; the topology optimization analysis including analyzing the analytic model of the press-formed part to leave the minimum elements that most highly contribute to the rigidity under specific load constraint and volume percentage conditions, a computer-implemented step of subjecting the analytic model to an analysis of reverse press forming back to a flat sheet, thus finding a rigidity contributable portion (71a, 41a) in a blank sheet corresponding to the rigidity contributable portion (71a, 41a) of the analytic model, a rigidity improving step of applying a rigidity improvement to the contributable portion (41a, 71a) of the blank sheet (41, 71) on a basis of the portion detected by the rigidity-contributable-portion detecting step, wherein the rigidity improving step performs one or more of increasing a thickness of the rigidity contributable portion (41a, 71a) of the blank sheet (41, 71) by blanking the rigidity contributable portion of the blank sheet and joining a sheet member formed from a thicker sheet and having the same shape as the rigidity contributable portion of the blank sheet, thus forming a tailored blank sheet, increasing a Young's modulus of the rigidity contributable portion of the blank sheet by blanking the rigidity contributable portion of the blank sheet and joining a sheet member having a higher Young's modulus and having the same shape as the rigidity contributable portion of the blank sheet, thus forming a tailored blank sheet, and bonding another sheet to the rigidity contributable portion of the blank sheet for reinforcement by welding or bonding with adhesive a sheet member of another sheet material formed into the same shape as the rigidity contributable portion of the blank sheet, thus forming a reinforced blank sheet, and a step of press-forming the tailored or reinforced blank sheet.