  The Serpens South embedded cluster, which is located at the constricted part
in a long filamentary infrared dark cloud, is believed to be in very early
stage of cluster formation. We present results of near-infrared (JHKs)
polarization observations toward the filamentary cloud. Our polarization
measurements of near-infrared point sources indicate a well-ordered global
magnetic field that is perpendicular to the main filament, implying that the
magnetic field is likely to have controlled the formation of the main filament.
On the other hand, the sub-filaments, which converge on the central part of the
cluster, tend to run along the magnetic field. The global magnetic field
appears to be curved in the southern part of the main filament. Such morphology
is consistent with the idea that the global magnetic field is distorted by
gravitational contraction along the main filament toward the northern part that
contains larger mass. Applying the Chandrasekhar-Fermi method, the magnetic
field strength is roughly estimated to be a few x 100 microgauss, suggesting
that the filamentary cloud is close to magnetically critical as a whole.
