An automatic transmission for a vehicle having a plurality of gear trains provided between an input shaft and an output shaft, comprises a hollow shaft coaxially including the input shaft, a forward drive gear rotatably mounted on the hollow shaft, a forward driven gear integrally mounted on the output shaft and constantly meshing with the forward drive gear, a reverse drive gear rotatably mounted on the input shaft, a changeover hub integrally mounted on the hollow shaft between the forward drive gear and the reverse drive gear, an first idler gear constantly meshing with the reverse drive gear, a second idler gear integrally formed with the first idler gear and constantly meshing with the forward driven gear and a changeover member provided between the forward gear and the reverse drive gear for engaging the changeover hub either with the forward drive gear or the reverse drive gear.