When an image forming job is completed that records onto a recording sheet an image formed on a photoconductor drum and conveys the recording sheet, a simple process control is carried out that forms some filled patch images with using some toners. After the simple process control is carried out, a determination is carried out, in accordance with a charge control value of a charge roller adjusted by the simple process control (a voltage value applied on the charge roller), whether a formal process control should be carried out or not that forms many patch images with using much toners. The formal process control is additionally carried out, when the determination means so.