  We calculate the A-dependence of charm and beauty production cross sections
on nuclear targets taking into account the difference of quark and gluon
distributions in free nucleons and in nucleus. At comparatively low energies,
if $\sigma \sim A^{\alpha}$, the value of $\alpha$ is slightly higher than
unity. With the growth of the initial energy the value of $\alpha$ decreases
and becomes smaller than unity. We also calculate the values of $\alpha$ for
different Feynman-$x$ of the produced $Q\overline{Q}$ pair and obtain that they
decrease significantly in the beam fragmentation region.
