To reduce the change of electrification property of a developer in a developing vessel from the initial stage to the end, by containing the two component developer including a carrier whose electrification property is lower than that of the carrier replenished from the developer replenishing port as the start developer at the initial setting time of the developer vessel use starting.

The developing vessel 41 provided with a developer replenishing port 42 and a developer discharging port 43 houses a developing roll 64, two component developer and the developer feeding members 61 to 63. The developer feeding members 61 feed the two component developer on the developing roll 64. Then, at the initial setting time of the use starting of the developer vessel 41, the two component developer including the same carrier as the feeding carrier, however the carrier whose electrification property is lowered by such as the toner adhesion, is contained in the developing vessel 41 as the start developer. In such a manner, the electrification property of the developer in the developing vessel 41 can be maintained unchanging, therefore the stable image quality can be maintained from the service start until the service life termination.