Abstract: An image pickup apparatus includes an optical system, a detector, and an image processor. The detector picks up an object image that passes through the optical system. The image processor performs a predetermined process for an object image signal obtained from the detector. A relative position between the optical system and the detector is set by adjusting an optical axis and/or a back focus in association with at least one of variation in quantity of ambient light around an image pickup area, variation in image circle, and variation in angle of view.