On the relativistic invariance of the continuity equation in quantum mechanics of the photon

This article provides important for the foundation of photon quantum mechanics the proof of relativistic invariance of the continuity equation for the probability density to detect the photon in configuration space in the case of plane monochromatic waves. Since waves of this kind initiate the occurrence of the majority of the observed interference phenomena, including in the Young's experiment, it is emphasized that their theoretical explanation from the point of view of photon quantum mechanics has relativistic invariant character.