Patent ID: 8626039

Claim:
An image forming apparatus for forming an image, comprising: an image bearer to bear a latent image on its surface; a developer container to accommodate developer, said developer having toner and magnetic carrier; and a developing device includes: a non-magnetic rotatable sleeve as a developer bearer to bear the developer on its surface; and a development electric field generator to generate a development electric field between the image bearer and the developer bearer by applying a development bias to the developer bearer, said developing device visualizing the latent image borne on the image bearer as a toner image with the toner of the developer in the development electric field, wherein said development bias is an AC bias that generates an AC electric field therebetween as the development electric field, wherein said magnetic carrier includes a plurality of fine particles each covered by a covering layer made of prescribed material having a volume resistivity equal to or more than 10 12 [Ω·cm] and having a prescribed particle diameter equal to or less than 100 [mm], each of said a plurality of fine particles having a total volume resistivity equal to or less than 10 5 [Ω·cm], said magnetic carrier having a total volume resistivity equal to or more than 10 12 [Ω·cm], wherein a direction of said AC electric field is alternated a prescribed number of times or more per unit of time during a development process by changing a frequency of said AC bias in accordance with a line speed [mm/s] of the image bearer.