A downsized differential assembly having a simple structure, which can be mounted easily on automobiles. The differential assembly comprises: a first gear as an internal gear; a second gear as an external gear; a first eccentric gear as an external gear meshed with the first gear; a second eccentric gear as an internal gear meshed with the second gear; a supporting member supporting the first eccentric gear and the second eccentric gear; a first motion translating mechanism translating revolving motion of the first eccentric gear into rotary motion of the first rotary shaft; and a second motion translating mechanism translating revolving motion of the second eccentric gear into rotary motion of the second rotary shaft. Gear ratios between the first gear and the first eccentric gear and between the second gear and the second eccentric gear are different, and the first rotary shaft and the second rotary shaft are rotated in opposite directions.