  We study the possibility that minor mergers resolve the loss cone depletion
problem, which is the difficulty occured in the coalescence process of the
supermassive black hole (SMBH) binary, by performing numerical simulations with
a highly accurate $N$-body code. We show that the minor merger of a dwarf
galaxy disturbs stellar orbits in the galactic central region of the host
galaxy where the loss cone depletion is already caused by the SMBH binary. The
disturbed stars are supplied into the loss cone. Stars of the dwarf galaxy are
also supplied into the loss cone. The gravitational interactions between the
SMBH binary and these stars become very effective. The gravitational
interaction decreases the binding energy of the SMBH binary effectively. As a
result, the shrink of the separation of the SMBH binary is accelerated. Our
numerical results strongly suggest that the minor mergers are one of the
important processes to reduce the coalescence time of the SMBH binary much less
than the Hubble time.
