An automatic transmission 20 includes: a Simpson type complex planetary gear train 25 including single pinion type first and second planetary gears 21 and 22 and single pinion type third and fourth planetary gears 23 and 24; first through fourth clutches C1 to C4; and first and second brakes B1 and B2. A first carrier 21c of the first planetary gear 21 is coupled to an input shaft 20i. A first ring gear 21r of the first planetary gear 21 is selectively connected to an output shaft 20o by the first clutch C1.