The present work deals with the mass of photon which creates a force at the contact point of reflection resulting in slight deviation of photon from its path after reflection. Only the mass of photon can cause deviation due to inertial force. If photon has no mass, it cannot deviate. It is also found that this deviation of photon depends on the angle of polarization plane of laser light with respect to reflecting mirror. Such variation in the angle of deviation by the plane of polarization proves that the mass of photon is neither in the centre of photon nor distributed uniformly but located off-centre (away from the centre of photon). This work proves that photon has mass and the most important part of this work is to discover that the mass of the photon is located off-centre (away from the centre of photon). This discovery explains Wave Particle Duality of electromagnetic radiations.