Fastening device for a backrest element of a backrest of a seat arrangement in a motor vehicle, wherein the backrest comprises two backrest elements arranged movably independently of each other about a pivot axis running transversely with respect to the direction of travel, wherein each backrest element comprises an outer bearing point and a central bearing point for forming the pivot axis, wherein the outer bearing point comprises a bearing axle secured on the backrest element and a counter bearing element secured on the body of the motor vehicle, wherein the bearing axle can be mounted in the counter bearing element in a preassembly position and in a final assembly position, wherein the bearing axle comprises an end portion for attaching to the backrest element, a cylindrical bearing portion for mounting in the final assembly position, a preassembly bearing portion and a plate-like end portion bounding the preassembly bearing portion axially on the end side, wherein the preassembly bearing portion has a rectangular guide portion with side surfaces, which are aligned parallel to each other, for mounting in the preassembly position, and an eccentrically integrally formed alignment portion, wherein the alignment portion is formed conically for the axial movement of the bearing axle from the preassembly position into the final assembly position and comprises an obliquely running sliding surface tapering towards the bearing portion and a counter bearing surface lying opposite the sliding surface, wherein the counter bearing element has a housing portion with a cylindrical bearing recess corresponding to the bearing portion and a rectangular first slot region for receiving the guide portion in the preassembly position, wherein the slot region has side surfaces which are designed for the sliding contact of the alignment portion during the movement from the preassembly position into the final assembly position, wherein the central bearing point comprises a bearing axle secured on the backrest element and a counter bearing element secured on the body of the motor vehicle, wherein the bearing axle can be mounted in the counter bearing element in a preassembly position and in a final assembly position and, for this purpose, comprises an end portion for attaching to the respective backrest element, a preassembly bearing portion with a rectangular guide portion for mounting in the preassembly position, and a cylindrical bearing portion for mounting in the final assembly position, wherein the counter bearing element is arranged in a central region in a transverse direction and comprises a housing portion for the mounting and receiving of two adjacently arranged bearing axles and, for this purpose, comprises two wall portions in each case having a cylindrical bearing recess assigned to the cylindrical bearing portions and in each case having a rectangular first slot region for receiving the respective guide portion in the preassembly position. wherein each backrest element comprises an outer bearing point and a central bearing point for forming the pivot axis, wherein the outer bearing point comprises a bearing axle secured on the backrest element and a counter bearing element secured on the body of the motor vehicle, wherein the bearing axle can be mounted in the counter bearing element in a preassembly position and in a final assembly position, wherein the bearing axle comprises an end portion for attaching to the backrest element, a cylindrical bearing portion for mounting in the final assembly position, a preassembly bearing portion and a plate-like end portion bounding the preassembly bearing portion axially on the end side, wherein the preassembly bearing portion has a rectangular guide portion with side surfaces, which are aligned parallel to each other, for mounting in the preassembly position, and an eccentrically integrally formed alignment portion, wherein the alignment portion is formed conically for the axial movement of the bearing axle from the preassembly position into the final assembly position and comprises an obliquely running sliding surface tapering towards the bearing portion and a counter bearing surface lying opposite the sliding surface, wherein the counter bearing element has a housing portion with a cylindrical bearing recess corresponding to the bearing portion and a rectangular first slot region for receiving the guide portion in the preassembly position, wherein the slot region has side surfaces which are designed for the sliding contact of the alignment portion during the movement from the preassembly position into the final assembly position, wherein the central bearing point comprises a bearing axle secured on the backrest element and a counter bearing element secured on the body of the motor vehicle, wherein the bearing axle can be mounted in the counter bearing element in a preassembly position and in a final assembly position and, for this purpose, comprises an end portion for attaching to the respective backrest element, a preassembly bearing portion with a rectangular guide portion for mounting in the preassembly position, and a cylindrical bearing portion for mounting in the final assembly position, wherein the counter bearing element is arranged in a central region in a transverse direction and comprises a housing portion for the mounting and receiving of two adjacently arranged bearing axles and, for this purpose, comprises two wall portions in each case having a cylindrical bearing recess assigned to the cylindrical bearing portions and in each case having a rectangular first slot region for receiving the respective guide portion in the preassembly position.