PURPOSE: To prevent excitation light from being made incident in a photomultiplier and to precisely read image information with high sensitivity for a long time by forming at least the light receiving surface of the photomultiplier of a material which intercepts the excitation light and transmits stimulated luminous light.

CONSTITUTION: At least the light receiving surface of the photomultiplier 16 is formed of the material which intercepts the excitation light 14 and transmits the stimulated luminous light. Therefore, unnecessary light such as the excitation light which disturbs precise reading of an image is certainly intercepted and a filter need not be made to intervene between a light guide 28 and the photomultiplier 16. As the result, the increase of a boundary by forming an adhesive layer is eliminated. Thus, the image can be precisely read with high sensitivity without the loss of the stimulated luminous light or an adverse effect caused by the adhesive layer. Besides, the anxiety of the deterioration of read accuracy and sensitivity caused by the secular deterioration of the adhesive layer or the like is reduced and the image is stably and precisely read for a long time.