A crash reinforcing member for a vehicle comprising a long body, the body including: a pair of opposed walls (11, 31, 51, 71) each having front and rear ends, a flat center flange (13, 33, 53, 73) disposed between the front ends of the walls, a pair of curved corners (12, 32, 52, 72) which connect the front ends of the walls and the center flange with each other, and a pair of outer flanges (14, 34, 54, 74) extending outward from the rear ends of both the walls, in which a transverse cross-section of the body has a hat-shaped opened cross-sectional shape which opens toward the rear ends of both the walls by the pair of walls, the center flange, the pair of curved corners and the pair of outer flanges, wherein, in a range from a center section to one end of the body in its longitudinal direction, the body is divided into a first section (P1, P21, P41, P61) which occupies the center section or a portion near the center section, a second section (P2, P22, P42, P62) which occupies the one end in the longitudinal direction and a portion near the one end, and a third section (P3, P23, P43, P63) which connects the first section and the second section with each other, a width of the center flange in the first section is wider than a width of the center flange in the second section, a cross-sectional height of the first section is higher than a cross-sectional height of the second section, and the third section is provided as a gradually changing portion which smoothly connects the first section and the second section with each other, characterized in that a cross-sectional area of each of the curved corners in the first section is narrower than a cross-sectional area of each of the curved corners in the second section, wherein a cross-section of each of the pair of curved corners is of an arc shape having a central angle of 90°, and when a cross-sectional radius of the curved corner in the first section is defined as "R1" and a cross-sectional radius of the curved corner in the second section is defined as "R2", a ratio (R1/R2) of the radius R1 and the radius R2 is set in a range of 1/2 to 1/5. a pair of opposed walls (11, 31, 51, 71) each having front and rear ends, a flat center flange (13, 33, 53, 73) disposed between the front ends of the walls, a pair of curved corners (12, 32, 52, 72) which connect the front ends of the walls and the center flange with each other, and a pair of outer flanges (14, 34, 54, 74) extending outward from the rear ends of both the walls, in which a transverse cross-section of the body has a hat-shaped opened cross-sectional shape which opens toward the rear ends of both the walls by the pair of walls, the center flange, the pair of curved corners and the pair of outer flanges, wherein, in a range from a center section to one end of the body in its longitudinal direction, the body is divided into a first section (P1, P21, P41, P61) which occupies the center section or a portion near the center section, a second section (P2, P22, P42, P62) which occupies the one end in the longitudinal direction and a portion near the one end, and a third section (P3, P23, P43, P63) which connects the first section and the second section with each other, a width of the center flange in the first section is wider than a width of the center flange in the second section, a cross-sectional height of the first section is higher than a cross-sectional height of the second section, and the third section is provided as a gradually changing portion which smoothly connects the first section and the second section with each other, characterized in that a cross-sectional area of each of the curved corners in the first section is narrower than a cross-sectional area of each of the curved corners in the second section, wherein a cross-section of each of the pair of curved corners is of an arc shape having a central angle of 90°, and when a cross-sectional radius of the curved corner in the first section is defined as "R1" and a cross-sectional radius of the curved corner in the second section is defined as "R2", a ratio (R1/R2) of the radius R1 and the radius R2 is set in a range of 1/2 to 1/5.