An endoscope system, including: an endoscope for picking up an image of a subject and outputting an image pickup signal of the image; an external processor having a post-signal processing circuit which processes the image pickup signal inputted from the endoscope and generates a video signal that can be outputted to a monitor; and an output detecting circuit for detecting the presence or absence of an output of the image pickup signal and the presence or absence of an output of the video signal.