| 摘要 |
PURPOSE: To prevent the toner scattering of developer at and after the second developing, to prevent the color of a multicolor image from being mixed, to prevent the intrusion of the first toner into the second and succeeding developing devices and to decrease the roughness of a high-light image by making developing bias have voltage waveform including a pulse having a pulse width equal to or below a specified value and setting the number of the pulses impressed within a specified number. CONSTITUTION: A second developing device 27 is provided with a non-magnetic shell 401 as a developing carrier at an aperture part facing a photoreceptive belt 21. The developing bias of the voltage waveform including a pulse area where the pulse whose pulse width is <=200μsec is alternately repeated more than once in the positive direction and negative direction is used, and the number of the pulse impressed per one change of the magnetic pole of a magnetic core 402 is set respectively to be within 10 for one direction of the positive direction and the negative direction in a developing area. The toner is scattered to the photoreceptive belt 21 from the developer of the non-magnetic shell 401 by the pulse in the negative direction, and unnecessary pulse on the photoreceptive belt 21 is returned to the shell 401 by the pulse in the positive direction. |
