  We report the result of the analysis of the light curve of a caustic-crossing
binary-lens microlensing event OGLE-2009-BLG-023/MOA-2009-BLG-028. Even though
the event was observed solely by survey experiments, we could uniquely
determine the mass of the lens and distance to it by simultaneously measuring
the Einstein radius and lens parallax. From this, we find that the lens system
is composed of M-type dwarfs with masses $(0.50\pm 0.07) \ M_\odot$ and
$(0.15\pm 0.02)\ M_\odot$ located in the Galactic disk with a distance of $\sim
1.8$ kpc toward the Galactic bulge direction. The event demonstrates that
physical lens parameters of binary-lens events can be routinely determined from
future high-cadence lensing surveys and thus microlensing can provide a new way
to study Galactic binaries.
