A radiation image information recording/reading apparatus for detecting phosphorescent light from a side opposite of radiation irradiation on a stimulable phosphor sheet is downsized. The radiation image information recording/reading apparatus comprises an image recording unit for recording radiation image information on the sheet by irradiating the radiation representing image information on the sheet, an excitation light main scan means for main scan of the sheet by excitation light, photoelectric detection means for detecting the phosphorescent light emitted from the sheet, vertical scan means, and erasing means for releasing residual energy from the sheet prior to recording another image on the sheet after reading the information from the sheet. In the apparatus, the excitation light main scan means comprises a linear light source emitting the excitation light in the form of fan beams, and the photoelectric detection means comprises a line sensor.