An automotive floor structure, comprising: a pair of side sills extending in a fore-and-aft direction on either side of a vehicle body; a front floor panel extending between the two side sills; and a pair of floor frames extending in the fore-and-aft direction below the front floor panel at positions spaced inward from the two side sills, respectively, in a lateral direction of the vehicle body, such that a battery unit is disposed between the two floor frames below the front floor panel, the automotive floor structure further comprising: a first cross member upper extending in the lateral direction and having ends attached to the two side sills, respectively; and a first cross member lower extending in the lateral direction below the front floor panel at a position under the first cross member upper, wherein the first cross member upper and the first cross member lower vertically sandwich the battery unit therebetween, and the first cross member lower has ends secured to the two floor frames, respectively, characterized in that the first cross member lower comprises a pair of bracket members fixed to undersides of the two floor frames, respectively, and extending downward from the undersides; and a cross member main body extending between the two bracket members in the lateral direction and attached to a lower end of each bracket member, wherein each bracket member is of a hollow box-like shape, and a collar member through which a mounting bolt is passed is fixedly disposed inside each bracket member. a pair of side sills extending in a fore-and-aft direction on either side of a vehicle body; a front floor panel extending between the two side sills; and a pair of floor frames extending in the fore-and-aft direction below the front floor panel at positions spaced inward from the two side sills, respectively, in a lateral direction of the vehicle body, such that a battery unit is disposed between the two floor frames below the front floor panel, the automotive floor structure further comprising: a first cross member upper extending in the lateral direction and having ends attached to the two side sills, respectively; and a first cross member lower extending in the lateral direction below the front floor panel at a position under the first cross member upper, wherein the first cross member upper and the first cross member lower vertically sandwich the battery unit therebetween, and the first cross member lower has ends secured to the two floor frames, respectively, characterized in that the first cross member lower comprises a pair of bracket members fixed to undersides of the two floor frames, respectively, and extending downward from the undersides; and a cross member main body extending between the two bracket members in the lateral direction and attached to a lower end of each bracket member, wherein each bracket member is of a hollow box-like shape, and a collar member through which a mounting bolt is passed is fixedly disposed inside each bracket member. a first cross member upper extending in the lateral direction and having ends attached to the two side sills, respectively; and a first cross member lower extending in the lateral direction below the front floor panel at a position under the first cross member upper, wherein the first cross member upper and the first cross member lower vertically sandwich the battery unit therebetween, and the first cross member lower has ends secured to the two floor frames, respectively, characterized in that the first cross member lower comprises a pair of bracket members fixed to undersides of the two floor frames, respectively, and extending downward from the undersides; and a cross member main body extending between the two bracket members in the lateral direction and attached to a lower end of each bracket member, wherein each bracket member is of a hollow box-like shape, and a collar member through which a mounting bolt is passed is fixedly disposed inside each bracket member.