To provide an image forming apparatus in which correction of various image formation parameters can be carried out appropriately without forming a test patch, and stabilized image quality can be secured even if an image formation job of large volume is executed.

The image forming apparatus comprises a screen processing section 2c performing false halftoning of output object data based on a threshold table 2d, and an image forming section 21 for forming a toner image on a photosensitive body based the image data subjected to screening and transferring the toner image onto a recording sheet. The image forming apparatus is further provided with a section 2k for measuring toner consumption at the image forming section 21, and a section 2l for correcting the threshold table 2d based on the toner consumption thus measured.