This invention realizes separate control for each memory area. Furthermore, the nitride-based composition may have the general crystalline structure of M\u2032aM\u2033bSicNd, where Al substitutes for Si within the crystalline structure and M is located within the crystalline structure substantially at the interstitial sites. A retention strap attached to the front wall of the bag serves to hold the drain tube in its coiled condition against the bag’s front wall. A predetermined voltage is applied between the first transparent electrode layer and the second transparent electrode layer, and the light emission layer emits light in accordance with the light quantity of the control light L.