A measuring device includes an actuator which holds a lens unit and moves the lens unit in the direction of the optical axis thereof. A test chart is photographed, with the lens unit being opposed to a reference image pickup device, and the lens unit is positioned at a just-focus position. The gap between the reference image pickup device and the lens unit at this time is reproduced, and an image pickup device, which is to be integrated, and the lens unit are opposed with this gap, and are fixed.