  Semileptonic and nonleptonic decays of the B_c meson to B_s and B mesons,
caused by the c\to s,d quark transitions, are studied in the framework of the
relativistic quark model. The heavy quark expansion in inverse powers of the
active c and spectator \bar b quark is used to simplify calculations while the
final s and d quarks in the B_s and B mesons are treated relativistically. The
decay form factors are explicitly expressed through the overlap integrals of
the meson wave functions in the whole accessible kinematical range. The
obtained results are compared with the predictions of other approaches.
