The mechanism of the charge generation process in a single layered organic photoconductor comprising charge generating pigments (CGM) dispersed in the solid solution matrix of charge transport media in binder was studied. This type of photoreceptor exhibited a unique bipolar photosensitivity. Since the major carrier in this system was the hole, the charge generation sites for both polarities were considered to be in different locations at the top surface of the layer when positively charged, and the interface between the conductive substrate when negatively charged. Considering the difference of sensitivities by charging polarities in the experimental result, a model of charge generation by photoexcitation of the CGM in the bulk layer and diffusion of the excited state with phonon assistance in the layer was suggested. By assuming the exponential decay of the energy by diffusion to be independent of the electric field, we could determine the parameters for both sensitivities for this system. The result of numerical analysis using light absorption coefficients corresponded well to the experimental result for the spectral sensitivities of both polarities.