A vehicle bottom structure for supporting a battery pack comprising: a pair of side members that are disposed on both sides of a vehicle in a width direction and extend in a front-rear direction of the vehicle; and a plurality of cross members that extend in the width direction of the vehicle, are joined to the side members at both end parts, and configured to support a bottom of the battery pack disposed under a floor panel between the side members, from below; and a front-rear direction reinforcing member that is joined on the cross members so as to extend in the front-rear direction of the vehicle and cross the cross members, characterized in that: the cross member and the front-rear direction reinforcing member are each a long member having a hat-shaped cross-section and including: a groove-shaped part (31c, 40c) including a bottom plate (35, 41) and upright plates (36, 42) formed on both ends of the bottom plate (35, 41) in the width direction; and a flange (31f, 40f) connected to an open end of the groove-shaped part (31c, 40c), and the front-rear direction reinforcing member has cutouts that are formed at positions of the upright plates to intersect with the cross member and formed in U-shapes along a convex shape of the groove-shaped part of the cross member, and the bottom plate of the groove-shaped part of the front-rear direction reinforcing member is disposed on and joined to the bottom plate of the groove-shaped part of the cross member. a pair of side members that are disposed on both sides of a vehicle in a width direction and extend in a front-rear direction of the vehicle; and a plurality of cross members that extend in the width direction of the vehicle, are joined to the side members at both end parts, and configured to support a bottom of the battery pack disposed under a floor panel between the side members, from below; and a front-rear direction reinforcing member that is joined on the cross members so as to extend in the front-rear direction of the vehicle and cross the cross members, characterized in that: the cross member and the front-rear direction reinforcing member are each a long member having a hat-shaped cross-section and including: a groove-shaped part (31c, 40c) including a bottom plate (35, 41) and upright plates (36, 42) formed on both ends of the bottom plate (35, 41) in the width direction; and a flange (31f, 40f) connected to an open end of the groove-shaped part (31c, 40c), and the front-rear direction reinforcing member has cutouts that are formed at positions of the upright plates to intersect with the cross member and formed in U-shapes along a convex shape of the groove-shaped part of the cross member, and the bottom plate of the groove-shaped part of the front-rear direction reinforcing member is disposed on and joined to the bottom plate of the groove-shaped part of the cross member. the cross member and the front-rear direction reinforcing member are each a long member having a hat-shaped cross-section and including: a groove-shaped part (31c, 40c) including a bottom plate (35, 41) and upright plates (36, 42) formed on both ends of the bottom plate (35, 41) in the width direction; and a flange (31f, 40f) connected to an open end of the groove-shaped part (31c, 40c), and the front-rear direction reinforcing member has cutouts that are formed at positions of the upright plates to intersect with the cross member and formed in U-shapes along a convex shape of the groove-shaped part of the cross member, and the bottom plate of the groove-shaped part of the front-rear direction reinforcing member is disposed on and joined to the bottom plate of the groove-shaped part of the cross member.