Provided is an image sensor unit (60) that comprises: a light source (25) that irradiates an illumination target with at least ultraviolet light in a main scanning direction; a condenser (32) that condenses light from the illumination target; an image sensor (75) that converts light that has been condensed by the condenser (32) into an electrical signal; and an ultraviolet light cutting part (65) that is disposed between the illumination target and the image sensor (75), cuts ultraviolet light out of light reflected by the illumination target and transmits therethrough fluorescence generated as a result of a fluorescent substance that has been applied to the illumination target being excited by the ultraviolet light. The image sensor (75) includes an ultraviolet light detecting unit (77) that detects light which is reflected by a reflective part and which is not transmitted through the ultraviolet light cutting part (65), such light being a portion of the ultraviolet light radiated from the light source (25).