1. An inspection apparatus comprising: an image pick-up unit provided with an optical video camera; an image obtaining unit which fetches a video image that contains a signal (noise) that is substantially independent of each frame of the video image obtained by picking up a video image of an inspection object by the image pick-up unit; a local alignment unit which locally aligns a plurality of frames of the video image with different time phases; a frame synthesizing unit which synthesizes the plurality of frames of the video image aligned by the local alignment unit for generating an image formed of the synthesized frames with an SN ratio higher than the SN ratio of each of the frames before frame synthesis; and an image output unit for displaying or recording an image formed of the synthesis frame generated by the frame synthesizing unit, wherein the image output unit displays simultaneously the image fetched from the optical video camera and the image formed of the synthesized frames generated by the frame synthesizing unit.