A drive transmission device, which is included in an image forming apparatus, includes a drive transmission body to which a drive force is applied from a driving source, and a rotary shaft having a press-in portion mounted on one end thereof in the axial direction. The press-in portion has multiple planes disposed parallel to an axial direction and configured to receive the drive transmission body. The multiple planes include upstream and downstream side planes disposed downstream from the upstream side plane in a press-in direction of the drive transmission body. The upstream and downstream side planes are aligned along the press-in direction of the drive transmission body and have respective distances different from each other from an axial center of the rotary shaft. A distance from the downstream side plane to the axial center is greater than a distance from the upstream side plane to the axial center.