  We investigate the Mott transitions in the multi-orbital Hubbard model at
half-filling by means of the self-energy functional approach. The phase
diagrams are obtained at finite temperatures for the Hubbard model with up to
four-fold degenerate bands. We discuss how the first-order Mott transition
points $U_{c1}$ and $U_{c2}$ as well as the critical temperature $T_c$ depend
on the orbital degeneracy. It is elucidated that enhanced orbital fluctuations
play a key role to control the Mott transitions in the multi-orbital Hubbard
model.
