A developer supplier includes a developer container and a main unit. The main unit includes a mounting section. The developer container includes a container body and a container shutter. The container body is formed with a developer discharge port. The container shutter covers or exposes the developer discharge port. The main unit includes a housing, a guide mechanism, a fastening portion, a locking portion, and a lock release portion. The developer container is mounted into the mounting section in a first orientation being guided by the guide mechanism, and subsequently the container body is rotated in a first rotational direction so that the developer container changes to a second orientation in which the developer discharge port communicates with the developer supply port. The lock release portion is permitted to release the locking of the developer container so that the container body rotates to return to the first orientation.