A digital still camera includes an aperture stop opening, a taking lens system, and a CCD pickup element. In a manual focus device, an iris shifting mechanism sets the aperture stop opening in an aperture stop unit with reference to a first light amount gravity center by shifting the aperture stop opening to the right relative to a lens optical axis, and sets the aperture stop opening with reference to a second light amount gravity center by shifting the aperture stop opening to the left. First and second sample pickup data are obtained by the CCD pickup element in the setting of the aperture stop opening at the two light amount gravity centers. A display panel displays first and second sample images according to the sample pickup data, to indicate a present deviation of the taking lens system from an in-focus position in simulation. A focusing ring is externally operable, for moving the taking lens system on the optical axis, and for actuation while the two sample images are checked visually, to position the taking lens system when the two sample images inform a reach to the in-focus position.