The analog-to-digital converter array 13 includes one analog-to-digital converter 210 for each row of photodetectors 120 in the photodetector array 11. The image-processing unit 14 includes the plurality of processing circuits 400 for performing high-speed image processing. The signal converter 17 combines the output signals from the analog-to-digital converter array 13 with output signals from the image-processing unit 14. Under control of the control circuit 15 and the signal conversion controller 19, the signal converter 17 downconverts the composite signal at an important timing to a frame rate suitable for display on the monitor 18 and subsequently displays the signal on the monitor 18.