  We study the decay constants of pseudoscalar and vector $B$ meson in the
framework of light-cone quark model (LCQM). We apply the variational method to
the relativistic Hamiltonian with the Gaussian-type trial wave function to
obtain the values of $\beta$ (scale parameter). Then with the help of known
values of constituent quark masses, we obtain the numerical results for the
decay constants $f_P$ and $f_V$, respectively. We compare our numerical results
with the existing experimental data.
