An apparatus comprising: an image sensing device having a plurality of pixels for receiving light from an object upon separating the light into respective ones of different color components; an optical guidance device for accepting light rays in different directions from the same part of the object and guiding the light rays to the image sensing device; and a phase-difference determining device for determining a phase difference in an output signal of the image sensing device with respect to each of the light rays accepted in the different directions by the optical guidance device, determination being performed based upon a signal obtained by combining output signals of pixels, among the plurality of pixels, that correspond to prescribed different color components.