1. An image forming apparatus comprising: a developer which is attachable to and detachable from an apparatus main body and which holds toner; an image forming section which forms a toner image using the toner held inside the developer; and a controller which executes a density control operation of forming a patch image using the toner held inside the developer and controlling an image forming condition for the image forming section based on a density detection result of the patch image, wherein the developer includes a memory which stores specific information regarding an attribute which is specific to the developer, the controller determines a mode of the density control operation based on the specific information read out from the memory, the memory stores, as the specific information, timing information regarding the timing at which the density control operation using the developer should be executed, and the controller executes the density control operation at the timing which is determined based on the timing information read out from the memory.