The Earth-limb gamma-ray emission is produced by the interactions between the Earth's atmosphere and high-energy cosmic-ray (CR) particles, predominantly protons. At sufficiently thin atmosphere at which the gamma-ray absorption by air is negligible, the Earth-limb gamma-ray measurement by the Fermi Gamma-ray Space Telescope can be used to obtain the properties of the primary CR between 60 GeV to 6 TeV. Our inferred CR spectrum can be compared to that directly measured by ATIC-2, CREAM, and PAMELA as being a broken power law with the break energy at a few hundred GeV per nucleon. This newly-discovered spectral feature may offer a clue to the origin of the observed high-energy Galactic CRs.