To investigate the anomalous transport property and the electronic structure near the Fermi level of Yb 4 As 3 , we have measured the temperature dependence of reflectivity spectra of Yb 4 (As 1 - x P x ) 3 (x=0, 0.05, 0.15) in the far-infrared region. In Yb 4 As 3 , a Drude-curve with very low carrier density and long relaxation time appears at temperatures below 70K. Coincidently, a peak appears around 15meV. The peak is considered to originate from the hybridization between Yb 3 + 4f-hole and 5d states on the Yb 3 + chain.