  The RCW 106 molecular cloud complex is an active massive star-forming region
where a ministarburst is taking place. We examined its magnetic structure by
near-IR polarimetric observations with the imaging polarimeter SIRPOL on the
IRSF 1.4 m telescope. The global magnetic field is nearly parallel to the
direction of the Galactic plane and the cloud elongation. We derived the
magnetic field strength of $\sim100$-$1600~\mu$G for 71 clumps with the
Davis-Chandrasekhar-Fermi method. We also evaluated the magnetic stability of
these clumps and found massive star-forming clumps tend to be magnetically
unstable and gravitationally unstable. Therefore, we propose a new criterion to
search for massive star-forming clumps. These details suggest that the process
enhancing the clump density without an increase of the magnetic flux is
essential for the formation of massive stars and the necessity for accreting
mass along the magnetic field lines.
