When a new development device is mounted, a control unit of an image forming apparatus identifies a development device type. When an identification result corresponds to a first development device containing a first amount of developer, an agitation member operates in a first mode. When the identification result corresponds to a second development device containing a second amount of developer higher than the first amount, the agitation member operates in a second mode. A second operation amount of the agitation member in the second mode is higher than a first operation amount of the agitation member in the first mode. A developer containing chamber of the development device is provided with a discharge opening from which the developer is discharged. The operations in the first and second modes are performed after a sealing member sealing the discharge opening is removed and also before a normal image forming process is executed.