  Hidden symmetry in Coulomb interaction is one of the mysterious problems of
modern physics. Additional conserved quantities associated with extra symmetry
govern wide variety of physics problems, from planetary motion till fine and
hyperfine structures of atomic spectra. In this paper we present a simple
derivation of hidden symmetry operator in relativistic quantum mechanics for
the Dirac equation in the Coulomb field. We established that this operator may
be reduced to the one introduced by Johnson and Lippmann. It is worthwhile to
notice that this operator was discussed in literature very rarely and so is not
known well among physicists and was omitted even in the recent textbooks on
relativistic quantum mechanics and/or quantum electrodynamics.
