  Semileptonic and leptonic B decays are analyzed in the framework of the
relativistic quark model. Special attention is payed to the decays involving
$\tau$ lepton. It is found that the calculated particular decay branching
fractions are consistent with available experimental data within error bars.
However, the predicted and recently measured ratios $R(D^{(*)})$ of the $B\to
D^{(*)}\tau\nu_\tau$ and $B\to D^{(*)}l\nu_l$ branching fractions differ by
1.75$\sigma$ for $R(D)$ and by 2.4$\sigma$ for $R(D^*)$.
