IMAGE FORMING APPARATUS

PROBLEM TO BE SOLVED: To improve processing efficiency of a detecting process of toner patches, reduce a necessary memory size, and reduce a toner concentration adjusting time.SOLUTION: The image forming apparatus includes: toner patch creation means; detecting means for detecting the concentration of toner patches; and toner concentration adjusting means for adjusting the toner concentration according to the detection result of the detecting means. The image forming apparatus substantially continuously detects, with an entire toner patch area including background parts between the toner patches defined as a single area; after previously speculating a concentration distribution of the respective toner patches on the basis of characteristics of reflected light from the toner and the toner patches and a patch layout, calculates the toner patch concentration; speculates the number of extra sampling backgrounds outside the tip toner patches and outside the rear-end toner patch to be measured; calculates a shift amount of the detection area from the speculated number of sampling and the actual detection result; and reduce the detection area according to the shift amount of the detection area.