An automatic transmission includes a first planetary gear set including first to third rotating elements; a second planetary gear set including fourth to sixth rotating elements; a third planetary gear set including seventh to sixth to ninth rotating elements; an input shaft constantly connected with the first rotating element; an output shaft constantly connected with the second rotating element; and at least five friction elements including a first friction element capable of locking a rotation of the eighth rotating element, a second friction element configured to selectively connect the second rotating element with the fifth rotating element, a third friction element configured to selectively connect the second rotating element with a second rotating member defined by the sixth and seventh rotating elements, a fourth friction element configured to selectively connect the fifth rotating element with the eighth rotating element, and a fifth friction element configured to selectively connect the first rotating element with the fifth rotating element. The automatic transmission achieves each of at least seven forward speed-ratios and one reverse speed-ratio, by a concurrent engagement of two friction elements which are selected from the five friction elements.