DEVELOPING DEVICE, IMAGE FORMING APPARATUS, AND DEVELOPING METHOD

PROBLEM TO BE SOLVED: To prevent carrier spent to extend the life of a developer.SOLUTION: A developing device 2 develops a toner image by using a two-component developer comprising a toner and a carrier and includes control means, as a CPU mounted on a control substrate 217, for reducing, in printing conditions in which carrier spent is likely to occur, a peripheral speed ratio that is a ratio of peripheral speeds of first and second developing sleeves 2a and 2b to a peripheral speed of an image carrier 7 (steps S2, and S3), further reducing, in the printing conditions in which carrier spent is likely to occur, the peripheral speed ratio to extend the life of a developer, and increasing, in parallel with the reduction, voltages applied to the first and second developing sleeves 2a and 2b to increase printing density so as not to change image density.