Patent ID: 7257336

Claim:
A developing device, including (a) a magnetic permeability detecting section for measuring magnetic permeability of developer containing toner and carriers, in order to obtain a magnetic permeability detection value, (b) a toner supplying section for supplying the toner according to comparison of the magnetic permeability detection value and a magnetic permeability reference value, (c) a developing section for developing, by using the toner, an electrostatic latent image formed on an image carrier; and (d) a developing density correcting section for correcting a developing density by correcting, according to the density of a test image formed by using the developing section, a developing bias of the developing section and/or a potential charged on the image carrier, said developing device, comprising: a magnetic permeability reference value adjusting section for adjusting the magnetic permeability reference value in cases where a correction amount by the developing density correcting section exceeds a predetermined ordinary range; and a developing density correction reference setting section for setting a correction reference of the developing density in the developing density correcting section according to the magnetic permeability reference value thus adjusted.