  Magnetization and energy gap of Kondo insulator YbB_{12} are calculated
theoretically based on the previously proposed tight-binding model composed of
Yb 5d$\epsilon$ and 4f $\Gamma_8$ orbitals. It is found that magnetization
curves are almost isotropic, naturally expected from the cubic symmetry, but
that the gap-closing field has an anisotropy: the gap closes faster for the
field in (100) direction than in (110) and (111) directions, in accord with the
experiments. This is qualitatively understood by considering the maximal
eigenvalues of the total angular momentum operators projected on each direction
of the magnetic field. But the numerical calculation based on the band model
yields better agreement with the experiment.
