In an image forming device, a holder unit is movable in a moving direction between an accommodated position and a pull-out position. A plurality of toner boxes are detachably attachable to the holder unit in one to one correspondence with the plurality of developing units. Each toner box is detachably attachable to the holder unit at the pull-out position. Each toner box includes: a toner container accommodating therein toner and formed with an opening through which toner in the toner container is to be supplied to each developing unit; and a shutter movable between an open position for opening the opening and a closed position for closing the opening. An operation assembly is provided at the holder unit and configured to move the shutter between the open position and the closed position.