An image forming device includes a support member and a plurality of operation members supported on the support member. The support member is movable relative to a main casing. A plurality of toner cartridges is detachably mounted on the support member, and each includes a casing formed with an opening for supplying toner to a corresponding developing unit and a shutter movable relative to the casing to selectively open and close the opening. Each operation member is operated in a direction substantially parallel to an axial direction of photosensitive drums to press one of the casing and the shutter, thereby moving the shutter relative to the casing in the direction to open the opening.