In a lower vehicle-body structure of an automotive vehicle comprising a pair of right-and-left side sills, a floor panel, and a first seat-attaching bracket supporting a front seat, an upper wall portion of the first seat-attaching bracket comprises an attachment portion to which the front seat is attached, a slant portion (connection portion) which extends downward from an outward-side edge side of the attachment portion, and a stepped-down portion which extends from the slant portion toward the side sill, and a bead which protrudes upward and extends from the slant portion toward the side sill in the vehicle width direction is provided at the stepped-down portion.