  We investiaged the optical properties of four-layer BaRuO$_{3}$, which shows
a fermi-liquid-like behavior at low temperature. Its optical conductivity
spectra clearly displayed the formation of a pseudogap and the development of a
coherent peak with decreasing temperature. Temperature-dependences of the
density $n$ and the scattering rate $1/\tau$ of the coherent component were
also derived. As the temperature decreases, both $n$ and $1/\tau$ decrease for
four-layer BaRuO$_{3}$. These electrodynamic responses were compared with those
of nine-layer BaRuO$_{3}$, which also shows a pseudogap formation but has an
insulator-like state at low temperature. It was found that the relative rates
of change of both $n$ and $1/\tau$ determine either metallic or insulator-like
responses in the ruthenates. The optical properties of the four-layer ruthenate
were also compared with those of other pseudogap systems, such as high $T_{c}$
cuprates and heavy electron systems.
