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, and the controller determines a mode of the density control operation based on the specific information read out from the memory.