The present invention relates to a cartridge for use with a digital printing device. A silicon oxide film having a thickness of 500 to 2,000 angstroms is used as the passivation film and the thickness is set to a value in response to the wavelength of the incident light to maintain a substantially constant reflectance. The comb has a concave-convex surface formed in a back face part of a comb main body, and the holes are formed in concave parts of the concave-convex surface. The movable unit is disposed corresponding to the conductive portions to electrically connect or disconnect the plurality of conductive portions to achieve the switch function.