An image sensing apparatus has an image sensing device. The image sensing device includes a photoelectric conversion element that photoelectrically converts an optical image to acquire image data, and a readout control unit that reads out, in accordance with a supplied readout rule, the image data acquired by the photoelectric conversion element. The image sensing device also includes an image scaling ratio selection unit that selects the scaling ratio of the image to be output, a readout scheme selection unit that selects, in accordance with the selected image scaling ratio, the readout scheme of the image data to be read out from the photoelectric conversion element by the readout control unit, and a readout rule supply unit that supplies, to the readout control unit, a readout rule corresponding to the readout scheme selected by the readout scheme selection unit.