  A long ($>100,000$ seconds) observation of the bright BL Lac object PKS
2155-304 has been carried out with the Narrow Field Instruments of the BeppoSAX
satellite as part of the Science Verification Phase. The source was detected
between 0.1 and about 100 keV at an intermediate intensity level compared to
previous observations. The unique spectral coverage of BeppoSAX has allowed us
to detect a number of spectral features. Between 0.1 and 10 keV the spectrum
can be well described by a convex spectrum with (energy) slope gradually
steepening from 1.1 to 1.6. At higher energies evidence for a sharp spectral
hardening is found, while in the soft X-rays (0.1-1.0 keV) some evidence for an
absorption feature was found. Indication for an emission line at 6.4 keV in the
source rest frame is present. Repeated variability of $\approx 20-30%$ around
the mean flux is clearly detected on time scales of a few hours. From the
symmetry and timescale of the observed variations we derive limits on the
magnetic field and on the maximum energy of the emitting particles, implying
that PKS 2155-304 should not be bright at TeV energies.
