  We performed optical spectroscopy and photometry of SN 2006gy at late time,
~400 days after the explosion, with the Subaru/FOCAS in a good seeing
condition. We found that the SN faded by ~3 mag from ~200 to ~400 days after
the explosion (i.e., by ~5 mag from peak to ~400 days) in R band. The overall
light curve is marginally consistent with the 56Ni heating model, although the
flattening around 200 days suggests the optical flux declined more steeply
between ~200 and ~400 days. The late time spectrum was quite peculiar among all
types of SNe. It showed many intermediate width (~2000 km/s FWHM) emission
lines, e.g., [Fe II], [Ca II], and Ca II. The absence of the broad [O I] 6300,
6364 line and weakness of [Fe II] and [Ca II] lines compared with Ca II IR
triplet would be explained by a moderately high electron density in the line
emitting region. This high density assumption seems to be consistent with the
large amount of ejecta and low expansion velocity of SN 2006gy. The H-alpha
line luminosity was as small as ~1x10^39 erg/s, being comparable with those of
normal Type II SNe at similar epochs. Our observation indicates that the strong
CSM interaction had almost finished by ~400 days. If the late time optical flux
is purely powered by radioactive decay, at least M_Ni ~ 3 M_sun should be
produced at the SN explosion. In the late phase spectrum, there were several
unusual emission lines at 7400--8800 AA and some of them might be due to Ti or
Ni synthesized at the explosion. (abridged)
