A disclosed developing device includes a toner carrying member having electrodes, a toner supply unit supplying the toner to the toner carrying member, and a hopping electric field generator unit generating electric field to cause the toner hopping on the toner carrying member by applying a pulse voltage to the electrodes. In one embodiment, a dummy gate is used. The planetary gear sets may each be of the single pinion type or double pinion type. The synchronization portion of the component video signal from the DVD player is sent to one of the input ports of the AV receiver as a trigger signal for comparison thereof with the synchronization signal in the switch box.