Magnetic field (H) effects on a correlated electron system with the
spin-state degree of freedom are examined. The effective Hamiltonian derived
from the two-orbital Hubbard model is analyzed by the mean-field approximation.
Applying H to the low-spin (LS) phase induces the excitonic insulating phase,
as well as the spin-state ordered phase where the LS and high-spin (HS) states
are ordered alternately. In the case where H is applied to the HS phase, a
reentrant transition for the HS phase appears. A rich variety of the phase
diagrams are attributed to the spin-state degree of freedom and their
combinations in the wave function as well as in the real-space configuration
