A developing device includes a developer cartridge and a developing unit. The developing unit includes a first guide and a second guide. The second is movable with respect to the developing frame between a first position where the second guide is in continuous with the first guide and a second position where a continuous state of the second guide with the first guide is interrupted. The developer cartridge includes a developer frame that accommodates a developer and a first guided member movable with respect to the developer frame. The first guide and the second guide at the first position guide the first guided member in the course of attaching the developer cartridge to the developing unit. When an attachment of the developer cartridge to the developing unit completes, the first guide receives the first guided member, and the second guide is at the second position.