1. An image capturing apparatus that carries out autofocus control by driving a focus lens, comprising: a detection unit which detects a region of a particular object from a captured image; a setting unit which sets a focus detection area based on detection results obtained by the detection unit; a generating unit which generates an AF evaluation value based on a component of a predetermined frequency band contained in the focus detection area of a captured image; a determination unit which determines an in-focus position search direction based on changes in a size of the region of the particular object detected by the detection unit; and a control unit which determines an in-focus position based on a plurality of AF evaluation values obtained at different positions of the focus lens by driving the focus lens to the different positions based on the in-focus position search direction determined by the determination unit based on the changes in the size of the region of the particular object detected.