  We observed the nearby galaxy M~51 (NGC 5194) with BeppoSAX. The X-ray
properties of the nucleus below 10 keV are almost the same as the ASCA results
regarding the hard component and the neutral Fe K$\alpha$ line, but the
intensity is about half of the ASCA 1993 data. Beyond this, in the BeppoSAX PDS
data, we detected a bright hard X-ray emission component which dominates above
10 keV. The 10 -- 100 keV flux and luminosity of this component are
respectively $2\times10^{-11}$ erg s$^{-1}$ cm$^{-2}$ and $2\times10^{41}$ erg
s$^{-1}$. These are about 10 times higher than the extrapolation from the soft
X-ray band, and similar to the flux observed with Ginga, which found a bright
power law component in 2 -- 20 keV band. Considering other wavelength
properties and the X-ray luminosity, together with strong neutral Fe K line,
the hard X-ray emission most likely arises from a low luminosity active
nucleus, which is obscured with a column density of $\sim10^{24}$cm$^{-2}$.
This suggests that hidden low luminosity AGNs may well be present in other
nearby galaxies. We interpret the discrepancy between Ginga and other X-ray
satellites to be due to a large variability of absorption column density toward
the line of sight over several years, suggesting that the Compton thick
absorption material may be present on a spatial scale of a parsec. Apart from
the nucleus, several ultra-luminous off-nuclear X-ray sources detected in M~51
exhibit long-term time variability, suggesting the state transition similar to
that observed in Galactic black hole candidates.
