  We report cosmic-ray proton and helium spectra in energy ranges of 1 to 120
GeV and 1 to 54 GeV/nucleon, respectively, measured by a balloon flight of the
BESS spectrometer in 1998. The magnetic-rigidity of the cosmic-rays was
reliably determined by highly precise measurement of the circular track in a
uniform solenoidal magnetic field of 1 Tesla. Those spectra were determined
within overall uncertainties of +-5 % for protons and +- 10 % for helium nuclei
including statistical and systematic errors.
