To improve the performance of a developing device when reproducing the developing device.

The method comprises the step of reinjecting developer into the developing device, that includes a developer carrier for holding a developer thereon and a layer thickness regulating member which is disposed in a contact part with the developer carrier and used to regulate the thickness of the layer of developer held on the developer carrier. The method also comprises the step of determining whether the relative position of the layer thickness regulating member to the developer carrier needs to be altered or not, based on data about the characteristics of the developer passed through the contact part with the developer carrier, the data being recorded in the developing device after the developer carrier and the lauer thickness regulating member are mounted on the developing device, and then altering the relative position when the determination is made that their relative position needs to be altered.