A mechanism that enables developer replenishment by a simpler structure and a mechanism that enables more user-friendly developer replenishment are provided. An attachment port to which a developer supply bottle containing a developer stored therein is detachably attachable is disposed in an interior of an image forming apparatus. The developer supply bottle can be attached when the cover is in an open state. According to this image forming apparatus, when the developer supply bottle is attached to the attachment port, the developer inside the developer supply bottle moves into a developer housing chamber by its own weight.