An imaging system according to the present invention is capable of outputting an image which is less unnatural while elongating a signal storage time of a CCD camera gradually. It includes an IR lamp for radiating an infrared ray, a CCD camera 5 for taking the place radiated by the IR lamp and converting it into an electric signal, and an image processing unit 7 capable of outputting an image with a different exposure value continuously and periodically, while varying a signal storage time of the CCD camera 5 at a predetermined period. The image processing unit 7 is characterized by outputting an image that is different in exposure depending upon a signal storage time according to the extent to which how strongly light strikes on the CCD camera 5, and elongating gradually the signal storage time when there is no strong light falling on CCD camera 5.