An automatic transmission has a first brake, a third brake and a hydraulic actuator for the third brake substantially axially aligned in sequence from rear to front in a radially outer area of the transmission. In addition, a first planetary gear unit, a first one-way clutch and a second one-way clutch are provided in an axial sequence from rear to front, in a radially inner area of the transmission. In this manner, component members are mounted with good spatial efficiency in both radial and axial dimensions. Furthermore, because a carrier of the first planetary gear is connected to a third brake through the first one-way clutch, the carrier can be reversely rotated by disengaging the third brake, enabling six forward speeds.