Radiation image read out device

A radiation image information read out device for reading out radiation image information recorded on a stimulable phosphor plate by scanning the stimulable phosphor plate with a stimulating ray comprising in combination a photodetector for detecting the light emitted by the stimulable phosphor plate upon stimulation of the stimulable phosphor, and a light guide member provided between the photodetector and the stimulable phosphor plate for transmitting the light emitted by the stimulable phosphor plate to the photodetector, said light guide member being made of a light transmitting sheet material one end of which is located adjacent to a scan line on the stimulable phosphor plate and the other of which is located adjacent to the light receiving face of the photodetector and shaped to be adapted to be adjacent to the light receiving face wherein said end to be located adjacent to the scan line is shaped into a linear form and the other to be located adjacent to the light receiving face of the photodetector is shaped into an annular form to be adapted for the light receiving face of the photodetector and wherein the ratio of a length from said one end to the other of the light guide member to a width of the end to be located adjacent to the scan line is within the range of 0.4 to 1.5.