To provide an automatic transmission having a planetary gear mechanism miniaturized by arrangement of the respective planetary gear mechanisms and respective clutches.

This automatic transmission has a first planetary gear mechanism P1, a second planetary gear mechanism P2, a first clutch 70 intermitting between a first input shaft 20 and a first output shaft 28 and a second clutch 90 intermitting between a second input shaft 40 and a second output shaft 48, on the common rotational axis, wherein the first clutch 70 and the second clutch 90 are automatically operated by an automatic shift driving means. In the automatic transmission having the planetary gear mechanism, the first clutch 70 and the second clutch 90 are arranged on the same side in the axial direction to the first planetary gear mechanism P1 and the second planetary gear mechanism P2.