  Variation of the von Neumann entropy by the Lorentz transformation is
discussed. Taking the spin-singlet state in the center of mass frame, the von
Neumann entropy in the laboratory frame is calculated from the reduced density
matrix obtained by taking the trace over 4-momentum after the Lorentz
transformation. As the model to discuss the EPR spin correlation, it is
supposed that one parent particle splits into a superposition state of various
pair states in various directions. Computing the von Neumann entropy and the
Shannon entropy, we have shown a global behavior of the entropy to see a
relativistic effect. We discuss also the super-relativistic limit,
distinguishability between the two particles of the pair and so on.
