Submitted to Phys.Rev.D.

lν decays, the slope of Isgur-Wise function and |V bc | value in potential quark model Abstract The modification of the naive potential model of the heavy meson is considered on the basis of the single-time prescription for the quark-meson form factor and the covariant choice of the quatk relative momentum. The application of the model to the description of the semileptonic decays of the beauty meson allows one to determine the Isgur-Wise function slope ρ 2 ≃ 1.25 and to extract the value |V bc | = 0.038 ± 0.003 from the experimental data.