In order to elucidate the photoprimary process of photochemical reaction of free radical photosensitive materials, the following investigations are made on N-phenyl-1-naphthylamine, diphenylaminetetrabromomethane, tribromomethane, dibromomethane systems by flash photolytic technique and fluoroandphosphori-metry; 1) the effect of dissolved oxygen on the fluorescence, phosphorescence and cationradical of the amine, 2) the relationship between the yield of the amine cation radical and the concentration of bromoalkane, 3) the relationship between the yield of the cation radical and the light intensity of flash, 4) the quenching effect of bromoalkane on the fluorescence of N-phenyl-l-naphthylamine, 5) etc. According to the results of these investigations, it is confirmed that the cation radicals are made by one photon process and from excited singlet species. Also it is concluded that the photoprimary process is exciplex formation between excited singlet state aromatic amine and ground state halogenated compound, charge separation in the complex and dissociation to amine cation radical and anion radical of halogenated compound.