In an automatic dual-clutch transmission, a lowest speed driven gear, other driven gears and a reverse gear are provided on a first output shaft to be freely rotatable. A 2nd speed driven gear and a highest speed driven gear are provided on a second output shaft to be freely rotatable. Further, the 2nd speed driven gear is provided with a large-diameter gear meshing with a 2nd speed drive gear and a small-diameter gear provided bodily with the large-diameter gear, being fewer in tooth number and smaller in diameter than the large-diameter gear, and meshing with the reverse gear. Thus, the automatic dual-clutch transmission is reduced in diameter by not having an output shaft dedicated to the reverse gear and is able to set the gear ratio for reverse to be large.