An image forming apparatus comprising: a paper feeding device feeding a recording medium; a printing device forming an image on the recording medium; a fusing device applying heat and pressure to the recording medium on which the image is formed by the printing device; and a discharge device discharging the recording medium passing through the fusing device, wherein at least one of the paper feeding device, the printing device, and the discharge device comprises a roller member transferring the recording medium and a power transmitting apparatus, wherein the power transmitting apparatus comprises: a driving source; a driving member rotated by the driving source; a driven member selectively linked with the driving member to rotate; a transmitting member disposed between the driving member and the driven member, the transmitting member being rotated by the driving member, axially moved along a rotation direction of the driving member so that the transmitting member is selectively connected to the driven member by coupling a protrusion to a groove corresponding to the protrusion; and an elastic member disposed between the transmitting member and the driven member, the elastic member providing an elastic bias into the transmitting member so that the transmitting member is selectively separated from the driven member, wherein a contact surface between the protrusion and the groove is inclined with respect to the rotation direction of the transmitting member so that the transmitting member is closely approached to the driven member. a paper feeding device feeding a recording medium; a printing device forming an image on the recording medium; a fusing device applying heat and pressure to the recording medium on which the image is formed by the printing device; and a discharge device discharging the recording medium passing through the fusing device, wherein at least one of the paper feeding device, the printing device, and the discharge device comprises a roller member transferring the recording medium and a power transmitting apparatus, wherein the power transmitting apparatus comprises: a driving source; a driving member rotated by the driving source; a driven member selectively linked with the driving member to rotate; a transmitting member disposed between the driving member and the driven member, the transmitting member being rotated by the driving member, axially moved along a rotation direction of the driving member so that the transmitting member is selectively connected to the driven member by coupling a protrusion to a groove corresponding to the protrusion; and an elastic member disposed between the transmitting member and the driven member, the elastic member providing an elastic bias into the transmitting member so that the transmitting member is selectively separated from the driven member, a driving source; a driving member rotated by the driving source; a driven member selectively linked with the driving member to rotate; a transmitting member disposed between the driving member and the driven member, the transmitting member being rotated by the driving member, axially moved along a rotation direction of the driving member so that the transmitting member is selectively connected to the driven member by coupling a protrusion to a groove corresponding to the protrusion; and an elastic member disposed between the transmitting member and the driven member, the elastic member providing an elastic bias into the transmitting member so that the transmitting member is selectively separated from the driven member, wherein a contact surface between the protrusion and the groove is inclined with respect to the rotation direction of the transmitting member so that the transmitting member is closely approached to the driven member.