  Magnetization curve and changes of the single-particle excitation spectra by
magnetic field are calculated for the periodic Anderson model at half-filling
in infinite spatial dimension by using the exact diagonalization method. It is
found that the field-induced insulator-to-metal transition occurs at a critical
field $H_c$, which is of the order of the single ion Kondo temperature. The
transition is of first order, but could be of second order in the infinite
system size limit. These results are compared with the experiments on the Kondo
insulator YbB$_{12}$.
