To provide an image pickup device capable of obtaining a high-quality monitor image from an image for focusing without complicating constitution, and its control method.

Luminous flux from an object is guided to an area sensor 106 from the mutually different pupil positions 101a and 101b of a photographing lens 101 through a field lens 103, a diaphragm 104 and a secondary image- formation lens 105 (a pair of lenses 105a and 105b), and a pair of picked-up image planes 106a and 106b having parallax that the pupil positions are different is obtained. A focal distance and a defocusing amount are measured by a focus detection part 109 from a pair of picked-up images related with a pair of picked-up image planes 106a and 106b, and the vignetting state of the picked-up image is detected by a vignetting detection part 112. The image having the smaller vignetting out of a pair of picked-up images is selected and switched by a display processing part 111, and outputted to a display part 113 so as to be displayed on a monitor.