To reduce the generation of vibration and noise.

A drive device comprises an oscillatory internally engaging planetary gear structure type reduction gear unit 102 formed such that a first and second axes 111 and 112 are situated on a central axis L and external tooth gears 115a and 115b are oscillatorily engaged with the outer periphery of the first shaft and an internal tooth gear 120 is provided to be internally engaged with an external tooth gear concentrically with the first shaft and a second shaft is coupled to the external tooth gear through a means to take out the rotation component of the external tooth gear; and a motor unit 103. A simple planetary roller mechanism 202 to transmit a rotation power through friction of a roller is located between the reduction gear unit and the motor unit. A mounting reference surface 261 to be vertical to the rotation directions of the rotary axes of a sun roller, a planetary roller, and a ring roller is formed at a casing to contain a simple planetary roller mechanism 202. A fixing means is provided to energize the ring roller to the mounting reference surface 261 and fix a ring roller 213 at a casing.