A focusing system includes a first drive unit for driving a first focus lens along the optical axis, a second drive unit for driving a second focus lens along the optical axis, a determining unit for periodically detecting a focus state of a subject image formed via the optical system and determining a focus position of the optical system based on the detected result, and a control unit for controlling the first and second drive units according to a result of determining the focus position of the optical system by the determining unit. The control unit controls the second drive unit to drive the second focus lens independently of the first focus lens, in the focus operation.