An ink delivery system having at least one off-axis ink supply container and an on-axis printhead assembly. A locking sleeve snaps onto the sensor portion and secures the sensor to the backing plate. The organic EL device employing the aromatic amine derivative reveals practically sufficient luminance even under low applied voltage, exhibits an enhanced efficiency of light emission, and is resistant to degrade even after a long time usage demonstrating a prolonged lifetime. The multi-layer structure functions as a wiring extending and existing in parallel on the surface of a semiconductor substrate, and an electric conduction film sends the current of a parallel direction on the surface of a semiconductor substrate. The compartments communicate with each other via a channel that is closed by an excess pressure vent device allowing gas at excess pressure to pass in one direction only from the smaller volume compartment to the larger volume compartment.