An automatic transmission includes: an input shaft connected to a driving source; an output shaft provided coaxially with the input shaft and connected to a differential mechanism; double pinion type first and second planetary gear sets; single pinion type third and fourth planetary gear sets; first to third clutches each configured to connect and disconnect predetermined rotational elements of the planetary gear sets to and from each other; and first and second brakes configured to connect and disconnect a predetermined rotational element of the planetary gear set to and from a transmission case. When the first to third clutches are engaged, and the first and second brakes are released, an eighth gear stage whose reduction ratio is 1 is formed.