An image pickup apparatus arranged to detachably mount a lens unit including a focus lens, controls such that if the focus lens is movable by the amount of movement within a predetermined time, a next amount of movement of the focus lens is decided on the basis of a first focus signal extracted from an image signal corresponding to charges accumulated in a focus detection area at a first timing, and if the focus lens is not movable by the amount of movement amount within the predetermined time, a next amount of movement of the focus lens is decided after completion of the movement of the focus lens on the basis of a second focus signal extracted from the image signal corresponding to the charges accumulated in the focus detection area at a second timing at which the focus lens is stopped.