A laser printer includes a coupling including an insert for transmitting driving force to a toner cartridge, a spring biasing the coupling, and a coupling receding arm positionally determining the coupling in a direction toward the toner cartridge. The coupling receding arm is formed of a single member and includes an arm portion in the form of a rod, an engagement rotated around the arm portion's longitudinal axis to move the coupling, and a lock lever connected to the arm portion and rotated around the arm portion's longitudinal axis to lock and unlock the toner cartridge.