A power transmitting device having a structure to allow a photoconductor to stably form a visible image on a printing medium. The power transmitting device interconnects a rotator and a drive motor, the drive motor generating drive power to drive the rotator. The power transmitting device includes at least one gear to be rotated upon receiving power from the drive motor, a rotating shaft having one end penetrating the gear and a coupler to interconnect the other end of the rotating shaft and the rotator. An outer diameter of the coupler, an outer diameter of the rotator and an outer diameter of the gear satisfy the following relation: 0.7D1