To enhance stability in maneuvering at a high speed while maintaining sufficient durability at the high speed by providing proper rigidity of a belt and proper reinforcement of the belt by a belt reinforcing layer.

This flat pneumatic radial tire is equipped with a tread part 1, a side wall part 2, a bead part 3, a radial carcass 5 provided in each bead part 3, and a belt 6 provided on the outer periphery side of the crown part of the radial carcass 5. Each side part of a belt layer 6a most adjacent to the radial carcass is folded back on the side part 6b on the further outer periphery side, and a belt reinforcing layer 10 to completely cover at least the folded part is provided. The width B of the folded part 6c of the belt layer is set for 8-13% of the maximum width A of the belt.