  Microlensing can provide an important tool to study binaries, especially
those composed of faint or dark objects. However, accurate analysis of
binary-lens light curves is often hampered by the well-known degeneracy between
close (s<1) and wide (s>1) binaries, which can be very severe due to an
intrinsic symmetry in the lens equation. Here s is the normalized projected
binary separation. In this paper, we propose a method that can resolve the
close/wide degeneracy using the effect of a lens orbital motion on lensing
light curves. The method is based on the fact that the orbital effect tends to
be important for close binaries while it is negligible for wide binaries. We
demonstrate the usefulness of the method by applying it to an actually observed
binary-lens event MOA-2011-BLG-040/OGLE-2011-BLG-0001, which suffers from
severe close/wide degeneracy. From this, we are able to uniquely specify that
the lens is composed of K and M-type dwarfs located at ~3.5 kpc from the Earth.
