An automatic transmission includes a first rotating element provided by coupling a sun gear of a second planetary gear set and a carrier of a third planetary gear set to each other, a second rotating element provided by coupling a carrier of the second planetary gear set and a ring gear of the third planetary gear set to each other, a third rotating element provided by a ring gear of the second planetary gear set, and a fourth rotating element provided by a sun gear of the third planetary gear set. The first rotating element and the second rotating element are coupled to a case by first and second brakes, the fourth and first rotating elements are coupled to a ring gear of a first planetary gear set via first and second clutches, the second and first rotating elements are coupled to an input shaft via third and fourth clutches, and the third rotating element is integrally coupled to an output gear, so that the automatic transmission can provide eight forward gear stages by changing a combination of two of the clutches and brakes which are engaged to each other.