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 $M=1526pm3(stat.)pm 3(syst.) MeV/c^2$ 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 ($uuddbar{s}$) baryon state. The total cross section for $Theta^+$ production in pN-interactions for $X_Fge 0$ was estimated to be $(30div120) mu b$ and no essential deviation from A-dependence for inelastic events $(sim A^{0.7})$ was found.
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