image processing unit 33 to the display device 5 the curvature detecting unit 36 detects a curvature of an optical fiber 41 specifically the curvature detecting unit detects a shape of the optical fiber 41 using a known pressure sensor or the like not illustrated detecting the shape of the optical fiber 41 and detects the curvature of the optical fiber 41 based on the detected shape the detection result of the curvature of the optical fiber 41 is output to the control unit 35 the control unit 35 transmits a control signal to the signal receiving unit 18 based on the detection result of the curvature detecting unit 36 specifically the control unit receives the detection result on a degree of curving of the optical fiber 41 from the curvature detecting unit 36 and transmits a control signal on characteristics of the output signal of the imaging element 15 to the signal receiving unit 18 via a signal line 42 the signal receiving unit 18 transmits the control signal transmitted from the control unit 35 to the imaging element 15 the imaging element 15 adjusts the characteristics of the output signal of the imaging element 15 based on the control signal that is the imaging element 15 adjusts an amplitude.