Patent ID: 7366457

Claim:
An image forming apparatus comprising: an image bearing member; a plurality of developing means which develop a yellow toner image with yellow toner, a magenta toner image with magenta toner, a cyan toner image with cyan toner or a black toner image with black toner on said image bearing member, one of said plurality of developing means being black toner developing means for developing a black toner image with black toner; transfer means for transferring toner images on said image bearing member onto a transferring material; cleaning means for cleaning residual toners on said image bearing member after said transfer means transfers the toner images; toner containing portion for collecting yellow toner, magenta toner, cyan toner or black toner cleaned by said cleaning means; a supply toner containing portion for containing black toner supplied to the black toner developing means; a first detection means for detecting a ratio of an amount of collected black toner in said toner containing portion to a total amount of toners in said toner containing portion; a second detection means which selects a least amount among an amount of collected yellow toner in said toner containing portion, an amount of collected magenta toner in said toner containing portion and an amount of collected cyan toner in said toner containing portion, and which detects the sum of the least amount, a first predetermined ratio corresponding to a first amount multiplied by the least amount and a second predetermined ratio corresponding to a second amount multiplied by the least amount to the total amount of toner in said toner containing portion; and changing means for changing a ratio of a supply amount supplied to the black toner developing means from said supply toner containing portion to a supply amount supplied to the black toner developing means from said toner containing portion, based on an output of said first detection means and an output of said second detection means.