To improve bending rigidity of a side sill against a load toward an inner side in a vehicle width direction during a lateral collision while suppressing a weight increase of thereof by providing minimum reinforcement, the side sill has a closed cross-sectional space extending in a vehicle longitudinal direction and includes a first upper reinforcing member that reinforces bending rigidity against a load toward the vehicle width inner side. The first upper reinforcing member is configured to be partially provided in a cross-sectional view that is perpendicular to a longitudinal direction of the side sill and to extend along a longitudinal direction of the side sill such that at least a part thereof overlaps a center pillar joined portion, to which a center pillar is joined, in a vehicle side view at a height position of the center pillar joined portion.