An imaging system includes an infrared lamp to emit infrared light, a CCD camera (5) to pick up an image of a place irradiated with the infrared lamp and convert the picked-up image into an electric signal, and an image processing unit (7) to periodically change a signal accumulation time of the CCD camera and periodically and continuously provide images of different exposure values. The image processing unit extracts a high-brightness block surrounded with a medium-brightness area from a first image of the periodically provided images, and according to a degree of the medium-brightness area, controls a signal accumulation time of a second image to be picked up.