A transmission device that includes a first shaft, a second shaft to which torque is transmitted from the first shaft via a torque transmitting mechanism, a tubular drive gear attached to the second shaft, and a driven gear that meshes with the drive gear, wherein the drive gear includes a plurality of outer teeth that are each meshed with a corresponding one of gear teeth of the driven gear and a fitting portion that is formed on an inner peripheral surface of the drive gear and that is fitted to the second shaft so that the drive gear rotates integrally with the second shaft.