To discriminate a portion to be measured from other portions in a luminal wall.

The probe 5 which applies excitation light to a living tissue and which receives radiation light generated from the living tissue caused by the excitation light includes: a tube 52 having a large-diameter aperture passage 52a and a small-diameter aperture passage 52b; an optical fiber 57 inserted into the large-diameter aperture passage 52a of the tube 52; an optical system 58 provided in the large-diameter aperture passage 52a for projecting the excitation light emitted from the distal end face of the optical fiber 57 to the living tissue outside the tube 52, and projecting the radiation light generated from the living tissue to the distal end face of the optical fiber 57; and a high-frequency electrode 55 inserted into the small-diameter aperture passage 52b at the distal end of the tube 52.