  As mentioned by Simone De Liberato [arXiv:1307.5615], when we suppose the
metallic thin mirror and perform the renormalization additionally to the
approach starting from the frequently-used system-environment coupling
Hamiltonian, we can certainly resolve the discrepancy of its result from that
obtained by the reliable approach in the main discussion of our paper [Phys.
Rev. A 88, 013814 (2013), arXiv:1301.3960]. Although the suggested approach is
currently applicable to the specific situation after checking its validity by
our reliable but cumbersome approach, we instead propose to start from the
system-environment coupling Hamiltonian determined properly by the mechanism of
the confinement and loss of the cavity fields. This approach is applicable to
any cavity structures in principle, and we do not face the renormalization
problem appearing in the comment.
