  The polarized optical reflectance spectra of the quasi two dimensional
organic correlated electron system $\kappa$-(BEDT-TTF)$_{2}$Cu[N(CN)$_{2}$]$Y$,
$Y =$ Br and Cl are measured in the infrared region. The former shows the
superconductivity at $T_{\rm c} \simeq$ 11.6 K and the latter does the
antiferromagnetic insulator transition at $T_{\rm N} \simeq$ 28 K. Both the
specific molecular vibration mode $\nu_{3}(a_{g})$ of the BEDT-TTF molecule and
the optical conductivity hump in the mid-infrared region change correlatively
at $T^{*} \simeq$ 38 K of $\kappa$-(BEDT-TTF)$_{2}$Cu[N(CN)$_{2}$]Br, although
no indication of $T^{*}$ but the insulating behaviour below $T_{\rm ins}
\simeq$ 50-60 K are found in $\kappa$-(BEDT-TTF)$_{2}$Cu[N(CN)$_{2}$]Cl. The
results suggest that the electron-molecular vibration coupling on the
$\nu_{3}(a_{g})$ mode becomes weak due to the enhancement of the itinerant
nature of the carriers on the dimer of the BEDT-TTF molecules below $T^{*}$,
while it does strong below $T_{\rm ins}$ because of the localized carriers on
the dimer. These changes are in agreement with the reduction and the
enhancement of the mid-infrared conductivity hump below $T^{*}$ and $T_{\rm
ins}$, respectively, which originates from the transitions between the upper
and lower Mott-Hubbard bands. The present observations demonstrate that two
different metallic states of $\kappa$-(BEDT-TTF)$_{2}$Cu[N(CN)$_{2}$]Br are
regarded as {\it a correlated good metal} below $T^{*}$ including the
superconducting state and {\it a half filling bad metal} above $T^{*}$. In
contrast the insulating state of $\kappa$-(BEDT-TTF)$_{2}$Cu[N(CN)$_{2}$]Cl
below $T_{\rm ins}$ is the Mott insulator.
