An image forming apparatus, comprising: a main body housing; an image carrier that is stored in the main body housing and has a circumferential surface on which an electrostatic latent image is formed; a developing device that has a first locking piece, is stored detachably in the main body housing and is adapted to supply a developer to the electrostatic latent image to develop the electrostatic latent image; a developer container that is stored detachably in the main body housing and is adapted to supply the developer to the developing device; an interference mechanism (454A, 510) that is adapted to disable the developing device from being removed from the main body housing, in a state where the developer container is mounted to the main body housing; and another unit stored in the main body housing, the another unit having a second locking piece; characterized by the developing device having a developing housing provided with a developer replenishing port, a shutter member capable of changing a posture thereof between a closing posture for covering the replenishing port and an opening posture for opening the replenishing port, and a biasing member for biasing the shutter member in a direction of the closing posture, the developer container has a pressing part that is adapted to interfere with the shutter member when the developer container is mounted to the main body housing and that is adapted to change the posture of the shutter member to the opening posture against the bias of the biasing member, the first locking piece is provided in the shutter member, the first locking piece and the second locking piece are configured to be brought into engagement with each other by changing the posture of the shutter member to the opening posture as a result of the interference between the pressing part and the shutter member that takes place when the developer container is mounted to the main body housing, and the engagement between the first locking piece and the second locking piece is configured to be released as the bias of the biasing member changes the posture of the shutter member to the closing posture when the interference between the pressing part and the shutter member is released as a result of removing the developer container from the main body housing. a main body housing; an image carrier that is stored in the main body housing and has a circumferential surface on which an electrostatic latent image is formed; a developing device that has a first locking piece, is stored detachably in the main body housing and is adapted to supply a developer to the electrostatic latent image to develop the electrostatic latent image; a developer container that is stored detachably in the main body housing and is adapted to supply the developer to the developing device; an interference mechanism (454A, 510) that is adapted to disable the developing device from being removed from the main body housing, in a state where the developer container is mounted to the main body housing; and another unit stored in the main body housing, the another unit having a second locking piece; the developing device having a developing housing provided with a developer replenishing port, a shutter member capable of changing a posture thereof between a closing posture for covering the replenishing port and an opening posture for opening the replenishing port, and a biasing member for biasing the shutter member in a direction of the closing posture, the developer container has a pressing part that is adapted to interfere with the shutter member when the developer container is mounted to the main body housing and that is adapted to change the posture of the shutter member to the opening posture against the bias of the biasing member, the first locking piece is provided in the shutter member, the first locking piece and the second locking piece are configured to be brought into engagement with each other by changing the posture of the shutter member to the opening posture as a result of the interference between the pressing part and the shutter member that takes place when the developer container is mounted to the main body housing, and the engagement between the first locking piece and the second locking piece is configured to be released as the bias of the biasing member changes the posture of the shutter member to the closing posture when the interference between the pressing part and the shutter member is released as a result of removing the developer container from the main body housing.