Patent ID: 7280773

Claim:
An image forming apparatus comprising: a developing unit configured to develop a latent image formed on an image carrier with toner to thereby produce a corresponding toner image; toner replenishing means including a removable toner cartridge for replenishing toner to said developing unit; toner content sensing means for sensing a toner content of a developer stored in said developing unit in terms of permeability of said developer; pattern density sensing means for sensing a reflection density of a reference pattern formed on said image carrier; and toner content control means for calculating, based on an output of said pattern density sensing means, a target value of said toner content sensing means and so controlling said toner replenishing means as to implement said target value; said toner content control means being capable of determining that said toner replenishing means has run out of toner and that the toner cartridge has been replaced; said toner content control means setting the target value for determining, after said developing unit has been driven for a preselected period of time since detection of a replacement of the toner cartridge, that a toner-end recovery operation is completed.