  SVD-2 experiment data have been analyzed to search for an exotic baryon
state, the $\Theta^+$-baryon, in a $pK^0_s$ decay mode at $70 GeV/c$ on IHEP
accelerator. The reaction $pA \to pK^0_s+X$ with a limited multiplicity was
used in the analysis. The $pK^0_s$ invariant mass spectrum shows a resonant
structure with $M=1526\pm3(stat.)\pm 3(syst.) MeV/c^2$ and $\Gamma < 24
MeV/c^2$. The statistical significance of this peak was estimated to be of $5.6
\sigma$. The mass and width of the resonance is compatible with the recently
reported $\Theta^+$- baryon with positive strangeness which was predicted as an
exotic pentaquark ($uudd\bar{s}$) baryon state. The total cross section for
$\Theta^+$ production in pN-interactions for $X_F\ge 0$ was estimated to be
$(30\div120) \mu b$ and no essential deviation from A-dependence for inelastic
events $(\sim A^{0.7})$ was found.
