A radiation image storage panel composed of a substrate and a layer of stimulable phosphor is prepared in an evaporation chamber kept at a pressure of 0.1 to 10 Pa by the steps of heating a source of the stimulable phosphor in the chamber so that the source is evaporated to give a gaseous product and depositing the gaseous product on the substrate which is arranged above the source to form the layer of stimulable phosphor on the substrate, in which the evaporation chamber has a diffusion preventing wall member surrounding a space between the source and the substrate, a top of which is positioned in the vicinity of a periphery of the substrate and a bottom of which is positioned in the vicinity of the source; and the diffusion preventing wall member is maintained at a temperature lower than a temperature of the source and higher than a temperature of the substrate.