  A probabilistic interpretation of one-particle relativistic quantum mechanics
is proposed. Quantum Action Principle formulated earlier is used for to make
the dynamics of the Minkowsky time variable of a particle to be classical.
After that, quantum dynamics of a particle in the 3D space obtains the ordinary
probabilistic interpretation. In addition, the classical dynamics of the
Minkowsky time variable may serve as a tool for "observation" of the quantum
dynamics of a particle. A relativistic analog of the hydrogen atom energy
spectrum is obtained.
