A power train of an automatic transmission with eight forward speeds and two reverse speeds includes: a speed reduction unit including a first variable input member connected to an input shaft via a first clutch, first and second variably stopped members connected to a transmission case, and a reduced speed output member; an output unit including a reduced speed input member connected to the reduced speed output member, second and third variable input members connected to the input shaft via second and third clutches, respectively, a third variably stopped member connected to the transmission case, and a shifted speed output member connected to an output gear. A first brake variably stops the third variable stopped member; a second brake variably stops the first variable stopped member; and a third brake variably stops the second variable stopped member.