  Temperature-dependent infrared reflectivity spectra of SrFe$_{4}$Sb$_{12}$
has been measured. A renormalized Drude peak with a heavy effective mass and a
pronounced pseudogap of 10 meV develops in the optical conductivity spectra at
low temperatures. As the temperature decreases below 100 K, the effective mass
($m^{*}$) rapidly increases, and the scattering rate ($1/\tau$) is quenched.
The temperature dependence of $m^{*}$ and $1/\tau$ indicates that the
hybridization between the Fe 3d spins and the charge carriers plays an
important role in determining the physical properties of SrFe$_{4}$Sb$_{12}$ at
low temperatures. This result is the clear evidence of the iron-based heavy
quasiparticles.
