  Taking account of a collective mode relevant to charge fluctuation, the
optical conductivity of spin-density-wave state has been examined for an
extended Hubbard model with one-dimensional quarter-filled band. We find that,
within the random phase approximation, the conductivity exhibits several peaks
at the frequency corresponding to the excitation energy of the commensurate
collective mode. When charge ordering appears with increasing inter-site
repulsive interactions, the main peak with the lowest frequency is reduced and
the effective mass of the mode is enhanced indicating the suppression of the
effect of the collective mode by charge ordering. It is also shown that the
reflectivity becomes large in a wide range of frequency due to the huge
dielectric constant induced by the collective mode.
