To provide a digital camera capable of causing a focus sensor to detect a focus while outputting to an image sensor image data for providing appropriate exposure after having adjusted an aperture ratio of an aperture in an image capture optical system such that appropriate exposure is achieved. A digital camera divides light from a subject having passed through an aperture into two beams of light; causes one of the beams to enter the image sensor to thus cause the image sensor to capture a subject image; and causes the other beam to enter the focus sensor to thus cause the focus sensor to detect a focus from the other beam of light. The digital camera adjusts an aperture ratio of the aperture such that the quantity of the other beam reaches the minimum quantity of light at or above which the focus sensor can detect a focus.