The image pickup apparatus of the present invention includes: an optical imaging system for forming an object image; an image pickup device including a plurality of pixels that photoelectrically converts the object image; a defocus quantity calculation section for calculating a defocus quantity based on a phase difference between a plurality of signals for focus detection obtained from a plurality of pixels for focus detection that respectively receive a light flux that passes through a different pupil region of the optical imaging system; a focusing section for driving the optical imaging system so as to achieve an in-focus state, in accordance with the defocus quantity calculated at the defocus quantity calculation section; an addition practicability determination section for determining a practicability of performing inter-frame addition on a plurality of signals for focus detection before calculating the defocus quantity, based on an analysis result of a signal component of the object image; and an inter-frame addition processing section for performing inter-frame addition based on a determination result of the addition practicability determination section.