A vehicle lower section structure comprising: a floor panel intended to configure part of a floor section of a vehicle body having a monocoque structure; a pair of left and right side members intended to configure part of a frame extending in a vehicle front-rear direction of the vehicle body, each side member including: a side member front extending straight along the vehicle front-rear direction as viewed along a vehicle vertical direction, and a side member rear joined to the floor panel at a vehicle lower side of the floor panel, and provided with an inflected portion extending from the side member front so as to spread out toward a vehicle width direction outward as viewed along the vehicle vertical direction; a power supply section disposed between the side members at a vehicle lower side of the floor panel and configured to supply power to a power unit installed at the vehicle; a crossing section running along the vehicle width direction between the inflected portions and configured to transmit load from one of the side members to the other of the side members in a case in which the one side member deforms toward the vehicle width direction inward; and a torque box disposed at the vehicle width direction outer side of the side member, characterized in that a vertical wall of the torque box at the vehicle rear of the torque box as viewed along the vehicle width direction is disposed at a position overlapping with a vertical wall at the vehicle rear of the crossing section, and is joined to the side member and to a rocker extending in the vehicle front-rear direction along a peripheral edge on the vehicle width direction outer side of the floor panel. a floor panel intended to configure part of a floor section of a vehicle body having a monocoque structure; a pair of left and right side members intended to configure part of a frame extending in a vehicle front-rear direction of the vehicle body, each side member including: a side member front extending straight along the vehicle front-rear direction as viewed along a vehicle vertical direction, and a side member rear joined to the floor panel at a vehicle lower side of the floor panel, and provided with an inflected portion extending from the side member front so as to spread out toward a vehicle width direction outward as viewed along the vehicle vertical direction; a side member front extending straight along the vehicle front-rear direction as viewed along a vehicle vertical direction, and a side member rear joined to the floor panel at a vehicle lower side of the floor panel, and provided with an inflected portion extending from the side member front so as to spread out toward a vehicle width direction outward as viewed along the vehicle vertical direction; a power supply section disposed between the side members at a vehicle lower side of the floor panel and configured to supply power to a power unit installed at the vehicle; a crossing section running along the vehicle width direction between the inflected portions and configured to transmit load from one of the side members to the other of the side members in a case in which the one side member deforms toward the vehicle width direction inward; and a torque box disposed at the vehicle width direction outer side of the side member, characterized in that a vertical wall of the torque box at the vehicle rear of the torque box as viewed along the vehicle width direction is disposed at a position overlapping with a vertical wall at the vehicle rear of the crossing section, and is joined to the side member and to a rocker extending in the vehicle front-rear direction along a peripheral edge on the vehicle width direction outer side of the floor panel.