IMAGE FORMING APPARATUS WHICH CONTROLS TONER ADHESION AMOUNT

An image forming apparatus forms test patches, and detects the adhesion amounts of toner in the test patches. The image forming apparatus calculates an approximate equation approximates the relationship between a developing bias and an adhesion amount of toner, based on the developing biases when the test patches were formed and the adhesion amounts of toner of the test patches. Distance between test patches is {(2n-1)/2} times of value L, where n is a natural number and L is a length of the photo conductor drum in a circumferential direction. The accuracy of toner adhesion amount control can be improved, and image density can be stabilized.