A closed cross-sectional structure member includes a hollow member, the hollow member having a collision side wall part located on a collision side, an opposed collision side wall part opposing the collision side wall part, a pair of first side wall part and second side wall part connecting with end portions of the collision side wall part and end portions of the opposed collision side wall part, a first inner wall part extending from the first side wall part to an inside of the hollow member, a second inner wall part extending from the second side wall part to the inside of the hollow member, a third inner wall part connecting with the first inner wall part and the collision side wall part, and a fourth inner wall part connecting with the second inner wall part and the collision side wall part.