  The spectral energy distribution (SED) of galaxies provides fundamental
information on the related physical processes. However, the SED is
significantly affected by dust in its interstellar medium. Dust is mainly
produced by asymptotic giant branch stars and Type II supernovae. In addition,
the dust mass increases through the metal accretion, and the grain size changes
by the collisions between the grains. The contribution of each process and the
extinction depend on the size distribution. Therefore, the SED model should
treat the evolution of the dust mass and size distribution. In spite of the
importance of dust evolution, many previous SED models have not considered the
evolution of the total mass and size distribution in a physically consistent
manner. In this work, we constructed a new radiative transfer SED model, based
on our dust evolution model consistent with the chemical evolution. To reduce
the computational cost, we adopted the mega-grain and the one-dimensional plane
parallel galaxy approximation. As a fiducial case, we calculated Milky Way-like
galaxy SEDs at various ages under the closed-box model. We found that a galaxy
at the age of 100~Myr does not produce small grains such as polycyclic aromatic
hydrocarbons. After 1~Gyr, we observed a drastic increase of infrared emission
and attenuation caused by a rapid increase of dust mass. This phenomenon can be
treated appropriately for the first time by our new model. This model can be
used for the SED fitting to a galaxy at any stage of evolution.
