  MWC 314 is one of the most luminous stars in the Milky Way. Its fundamental
parameters are similar to those of LBVs, although no large photometric
variations have been recorded.
  We analyzed the radial velocity (RV) variations displayed by the absorption
lines from the star's atmosphere using high resolution optical spectra. The RV
and profile variations of some permitted and forbidden emission lines of
metallic ions and the behavior of the Balmer and HeI lines has been
investigated as well.
  The RV of the absorption lines clearly shows a 60-day periodicity. A dense
coverage of the RV curve allowed us to derive accurate orbital parameters. The
RV of the FeII emission lines varies in the same way, but with a smaller
amplitude. Additionally, the intensity ratio of the blue/red peaks of these
emission lines correlates with the RV variations. The Balmer lines and {NII]
lines display a nearly constant RV and no profile variations in phase with the
orbital motion instead. The HeI-5876 \AA\ line shows a strongly variable
profile with broad and blue-shifted absorption components reaching velocities
of <-1000 km/s at some specific orbital phases. Our data strongly suggest that
the object is a binary system composed from a supergiant B[e] star and an
undetected companion. The emission lines with a non-variable RV could originate
in a circumbinary region. For the FeII emission lines we propose a simple
geometrical two-component model where a compact source of FeII emission, moving
around the center of mass, is affected by a static extra absorption that
originates from a larger area. Finally, the blue-shifted absorption in the
HeI-5876 \AA\ line could be the result of density enhancements in the primary
star wind flowing towards the companion that is best observed when projected
over the disk of the primary star.
