Disclosed is a light-emitting element having a light-emitting layer which includes a first layer, a second layer, and a third layer provided in this order on an anode side between the anode and a cathode. With being displaced vertically relative to the fixed electrode, the movable electrode is vibrated. A transmission timing control section determines a transmission start timing, at which to start the packet transmission, to be a timing obtained by delaying a reference timing by the delay amount selected by the delay amount determining section. The geometricsize characteristics of the links and of the sliding bearings make it possible to improve the stability and the resistance to fatigue and wearing of the articulated joints of the track. This makes it possible to fix the polarity of the voltage to be applied to the discharge lamp 8 to the single side polarity closer to the DC output operation.