There are two basic methods by which developed silver image can be formed, these are called chemical and physical development, respectively. In ordinary development, these both types of development may occur, when the solutions contain substances which have some solvent action on silver bromide. Authors tried to indicate the rate of physical development which occured in specific photographic development by the relative ratio of effective specific gravity of this developed silver grain to the effective specific gravity of completely physical developed silver, in accordance with synthetic consideration from three different types of experiments. These experiments are (1) observation of filamentary structure of developed silver grains of process-film by six types of test developer from post-fixation physical developer to inorganic chemical developer, (2) quantitative analysis of reduced silver amounts of developed layer by each test developer after sensitometrical exposure, and (3) measurements of average grain diameter of developed silver reduced by each six types of test developers, based on the electronmicroscopy of ultra-thin cross-sections of developed layer.