  NdO$_{0.5}$F$_{0.5}$BiS$_{2}$ is a new layered superconductor. We have
studied the low-lying electronic structure of a single crystalline
NdO$_{0.5}$F$_{0.5}$BiS$_{2}$ superconductor, whose superconducting transition
temperature is 4.87K, with angle-resolved photoemission spectroscopy. The Fermi
surface consists of two small electron pockets around the X point and shows
little warping along the $k_z$ direction. Our results demonstrate the
multi-band and two-dimensional nature of the electronic structure. The good
agreement between the photoemission data and the band calculations gives the
renormalization factor of 1, indicating the rather weak electron correlations
in this material. Moreover, we found that the actual electron doping level and
Fermi surface size are much smaller than what are expected from the nominal
composition, which could be largely explained by the bismuth dificiency. The
small Fermi pocket size and the weak electron correlations found here put
strong constraints on theory, and suggest that the BiS$_2$-based
superconductors could be conventional BCS superconductors mediated by the
electron-phonon coupling.
