An automatic transmission includes first to third planetary gear mechanisms; a second sun gear, a second carrier, and a second ring gear in a velocity diagram being defined as a first element, a second element, and a third element, respectively, in a case where a single pinion type planetary gear mechanism is applied as the second planetary gear mechanism; and the second carrier, the second ring gear, and the second sun gear in a velocity diagram being defined as the first element, the second element, and the third element, respectively, in a case where a double pinion type planetary gear mechanism is applied as the second planetary gear mechanism. A first brake fixes a first sun gear to a housing, a second clutch connects the first sun gear and the third element, and a fourth clutch connects the second element and a third carrier when a reverse speed is established.