A method employing a porous material sheet which has at predetermined positions plural dots each being composed of a group of probe molecules and a stimulable phosphor sheet having a phosphor layer which contains a stimulable phosphor in an amount of 10 to 140 g/m.sup.2 is favorably utilized to detect by autoradiography radioactively labeled substances originating from living body or its analogues which are able to be fixed to the probe molecules by biochemically specific binding reaction.