  Infrared Imaging Surveyor (IRIS) is a satellite which will be launched at the
beginning of 2003. One of the main purposes of the IRIS mission is an all-sky
survey in the far-infrared region with a flux limit much deeper than that of
IRAS. Detection of a large number of galaxies ($\sim several \times 10^6$ in
the whole sky) is expected in this survey. We investigated the expected optical
and near-infrared (NIR) number counts of galaxies detected by the far-infrared
scanner (FIS) of IRIS (hereafter, IRIS galaxies) and possibility of optical and
NIR follow-up of them. The spectral energy distribution and the luminosity
function of the IRIS galaxies are modeled based on the properties of galaxies
observed by IRAS. The IRIS galaxies are divided into two populations according
to their infrared luminosities ($L_{IR}$); normal spirals ($L_{IR}<10^{10}\LO$)
and starbursts ($L_{IR}>10^{10}\LO$). The expected number counts of IRIS
galaxies for both of the populations are calculated in $B$ and $H$ bands. We
show that about 60 normal galaxies and about 80 starburst galaxies are detected
per square degree in both of the two bands, when galaxy evolution is not taken
into account. All of the normal population of IRIS galaxies are located at the
redshift $z\ltsim 0.1$. As for the starburst population, we also calculated
number of galaxies with a simple model of evolution. The total number of
starburst population predicted by the evolution model is larger by 20% than
that expected from the non-evolution model. In the evolution model, the numbers
of low-z ($z<1$), intermediate-z ($1<z<3$), and high-z ($z>3$) galaxies are
100, 20, and 0.2 per square degree, respectively.
