An image forming apparatus comprising: a drum-shaped image bearer; a rotary member (9a, 9c) disposed around the drum-shaped image bearer; and a drive unit configured to rotate the drum-shaped image bearer and the rotary member (9a, 9c) disposed around the drum-shaped image bearer, the drive unit comprising: a drive source; an output gear driven by the drive source, wherein the drive unit comprises: a first gear greater in diameter than the output gear and disposed to engage the output gear; a first joint member projecting from a rotation center of the first gear coaxially with the first gear and coupled to a rotation center of the first rotary member; a second gear disposed between the first gear and the first joint member, characterized in that the second gear is united to a center of rotation of the first gear and to the first joint member coaxially therewith, the second gear smaller in diameter than the first gear; a driven gear to engage the second gear to be driven thereby, the driven gear smaller in diameter than the first gear and disposed within an area of the first gear in a radial direction thereof; and a second joint member projecting coaxially from a rotation center of the driven gear in a direction in which the first joint member projects and connected to a rotation center of the rotary member (9a, 9c), wherein the rotary member (9a, 9c) disposed around the drum-shaped image bearer receives the driving force from the second joint member projecting from the driven gear that meshes with the second gear united to the axial center of the first gear. a drum-shaped image bearer; a rotary member (9a, 9c) disposed around the drum-shaped image bearer; and a drive unit configured to rotate the drum-shaped image bearer and the rotary member (9a, 9c) disposed around the drum-shaped image bearer, the drive unit comprising: a drive source; an output gear driven by the drive source, wherein the drive unit comprises: a first gear greater in diameter than the output gear and disposed to engage the output gear; a first joint member projecting from a rotation center of the first gear coaxially with the first gear and coupled to a rotation center of the first rotary member; a second gear disposed between the first gear and the first joint member, characterized in that the second gear is united to a center of rotation of the first gear and to the first joint member coaxially therewith, the second gear smaller in diameter than the first gear; a driven gear to engage the second gear to be driven thereby, the driven gear smaller in diameter than the first gear and disposed within an area of the first gear in a radial direction thereof; and a second joint member projecting coaxially from a rotation center of the driven gear in a direction in which the first joint member projects and connected to a rotation center of the rotary member (9a, 9c), wherein the rotary member (9a, 9c) disposed around the drum-shaped image bearer receives the driving force from the second joint member projecting from the driven gear that meshes with the second gear united to the axial center of the first gear. a drive source; an output gear driven by the drive source, wherein the drive unit comprises: a first gear greater in diameter than the output gear and disposed to engage the output gear; a first joint member projecting from a rotation center of the first gear coaxially with the first gear and coupled to a rotation center of the first rotary member; a second gear disposed between the first gear and the first joint member, characterized in that the second gear is united to a center of rotation of the first gear and to the first joint member coaxially therewith, the second gear smaller in diameter than the first gear; a driven gear to engage the second gear to be driven thereby, the driven gear smaller in diameter than the first gear and disposed within an area of the first gear in a radial direction thereof; and a second joint member projecting coaxially from a rotation center of the driven gear in a direction in which the first joint member projects and connected to a rotation center of the rotary member (9a, 9c), a first gear greater in diameter than the output gear and disposed to engage the output gear; a first joint member projecting from a rotation center of the first gear coaxially with the first gear and coupled to a rotation center of the first rotary member; a second gear disposed between the first gear and the first joint member, characterized in that the second gear is united to a center of rotation of the first gear and to the first joint member coaxially therewith, the second gear smaller in diameter than the first gear; a driven gear to engage the second gear to be driven thereby, the driven gear smaller in diameter than the first gear and disposed within an area of the first gear in a radial direction thereof; and a second joint member projecting coaxially from a rotation center of the driven gear in a direction in which the first joint member projects and connected to a rotation center of the rotary member (9a, 9c), wherein the rotary member (9a, 9c) disposed around the drum-shaped image bearer receives the driving force from the second joint member projecting from the driven gear that meshes with the second gear united to the axial center of the first gear.