PURPOSE: To achieve bias impressing, to make lead wire processing easier, to minimize bias impression space, to reduce the number of parts and to reduce cost by providing a sliding plate on the driving shaft of a developing roller.

CONSTITUTION: The conductive driving shaft 6 of the developing roller 2 is rotatably born on the developing device main body 1 of a bias impressing mechanism. The driving shaft 6 is mounted so that it penetrates the outside surface of the main body 1. A fixing plate 13 for bias impressing and a conductive rotating and sliding plate 14 facing and brought into contact with the fixing plate 13 are provided and are made to press-bond with the driving shaft 6. The driving shaft 6 of the developing roller 2 is provided with the sliding plate 14, whereby bias impressing can be achieved without impressing a bias on a fixing shaft. Lead wire processing is made easier only by connecting a lead wire 24 to the fixing plate 13 on the side same as a power source connector 19. The longitudinal dimension of the developing roller can drastically be smaller and the number of the parts can be reduced, thereby reducing cost.