A focus adjustment device comprising an imaging unit that outputs image signals corresponding to images by an optical system; a focus detection unit that performs focus detection processes to detect focal states of the optical system; an aperture that restricts light beams to the imaging unit; an aperture drive unit; an initiation unit that initiates the focus detection process by the focus detection unit; a focused state determination unit that determines repeatedly whether the focal state of the optical system is a focused state or not based on a focus detection result when the initiation of the focus detection process is being performed; a mode set unit that sets motion picture imaging modes; and a control unit that controls the focused state determination when aperture is being driven, wherein the control unit allows the focused determination process when the aperture is driven if motion picture imaging mode is set.