When an imaging mode is set, a subject is imaged, and image data representing a subject image is obtained. Continuous AF is operated such that the subject image represented by the obtained image data is focused. Ranges ahead of and behind the focusing position of an imaging lens obtained in the continuous AF are determined as a focusing range. A formal search is conducted in the determined focusing range. A focusing position is determined from a graph of focusing integrated values obtained in the formal search. The imaging lens is put at the determined focusing position.