This invention includes an image sensor in which image forming pixels and focus detecting pixels which receive light beams from the exit pupil of the imaging lens which is partly light-shielded are arranged, the first vertical output line which outputs a signal from the image forming pixel in the vertical direction of the image sensor, a second vertical output line which outputs a signal from the focus detecting pixel in the vertical direction of the image sensor, a vertical addition unit which adds signals from a plurality of image forming pixels in the vertical direction, and a control unit which controls the vertical addition unit to add only signals from image forming pixels excluding focus detecting pixels, when the focus detecting pixels are included in targets for addition in the addition readout mode of making the vertical addition unit add signals from a plurality of image forming pixels.