An electrophotographic single layer organic photoreceptor consisting of relatively low concentrations of phthalocyanine pigments dispersed in an insulating binder polymer, which is generally referred to as a high gamma photoreceptor, shows the induction effect. Several mechanisms have been proposed to explain this phenomenon. However it is not completely clear at this time. In this paper, the photo-induced and dark discharge characteristics of the high gamma photoreceptors consisting of x-type metal-free phthalocyanine pigment and polyester polymer are found to be well described by our theoretical model which takes into account the structural trap. We have found that the good charge acceptance and the high gamma characteristics depend on structural traps. It is mathematically simulated that the x-type metal-free phthalocyanine's own photoresponse to digital image exposure is not deteriorated in spite of charge carrier trappings by structural traps during carrier transport.