An imaging system includes: an image sensor sensitive to ultraviolet light and visible light; a lens configured to focus light from a subject onto the image sensor; and an image processor configured to process image signals output from the image sensor. The image processor obtains the difference between image signals A1 and A2 output from the image sensor at times t1 and t2, respectively. If the differential signal A3 is greater than or equal to a predetermined value, the image processor determines that light from the subject contains the ultraviolet light, and generates an image signal CI based on the differential signal A3.