An image forming device includes a main casing, a photosensitive drum unit and a developing device unit. The photosensitive drum unit includes a plurality of photosensitive drums that forms electrostatic images thereon, each photosensitive drum having an axis, the plurality of photosensitive drums being juxtaposed along a line extending in a first direction orthogonal to the axis. The developing device unit includes a plurality of developing devices and a supporting member. The developing devices are disposed in one-to-one correspondence with the plurality of photosensitive drums, each developing device including a developing roller that supplies toner to corresponding photosensitive drum to develop the electrostatic images formed thereon and having a shaft extending in a second direction parallel to the axis of the photosensitive drum. The supporting member supports the plurality of developing devices to be movable between a first position for supplying toner to corresponding photosensitive drums and a second position retracted from the first position. The developing device unit is detachable from the main casing by moving the plurality of developing devices to the second position and drawing the supporting member.