A hat member 1 includes a top-plate portion 13, first ridges 113, and two side walls 11. The two side walls have a middle hardness Dc of 300 HV or higher. Each of the two side walls 11 includes a softened portion L and a strength-transition portion T adjacent to the softened portion L. The softened portion L has a hardness Dn lower than the middle hardness Dc by at least 8% (Dc−Dn≥0.08Dc). The strength-transition portion T extends 0.5 mm or longer from the softened portion L toward the first end of the side wall. The strength-transition portion T has a hardness Dt that transitionally changes within the range of 8% to 1% lower than the middle hardness Dc (0.92Dc≤Dt≤0.99Dc). The hat member 1 further includes two second ridges 114 and two flanges 14.