  We report on the 20 ksec observation of Vela X-1 performed by BeppoSAX on
1996 July 14 during its Science Verification Phase. We observed the source in
two intensity states, characterized by a change in luminosity of a factor ~ 2,
and a change in absorption of a factor ~ 10. The single Narrow Field Instrument
pulse-averaged spectra are well fit by a power law with significantly different
indices. This is in agreement with the observed changes of slope in the
wide-band spectrum: a first change of slope at ~ 10 keV, and a second one at ~
35 keV. To mimic this behaviour we used a double power law modified by an
exponential cutoff --- the so-called NPEX model --- to fit the whole 2-100 keV
continuum. This functional is able to adequately describe the data, expecially
the low intensity state. We found an absorption-like feature at ~ 57 keV, very
well visible in the ratio performed with the Crab spectrum. We interpreted this
feature as a cyclotron resonance, corresponding to a neutron star surface
magnetic strength of 4.9 x 10^12 Gauss. The BeppoSAX data do not require the
presence of a cyclotron resonance at ~ 27 keV as found in earlier works.
