A fluorescent light temperature sensor for producing a temperature signal from a fluorescent light of an optically stimulated fluorescent material is provided with: an LED for projecting light onto the fluorescent material; a driving circuit for driving the light projecting element; a photo diode for receiving the fluorescent light that is emitted from the fluorescent material; a signal processing circuit for producing the temperature signal from the output signal from the photo diode; and an APC circuit for controlling the driving of the driving circuit so as to maintain a uniform light projecting intensity from the LED based on the output signal of the photo diode.