An automatic transmission (10) includes an input shaft (12), an output (an output shaft 13) arranged coaxially with the input shaft and engaged with a differential mechanism, first and second planetary gear sets (PG1 and PG2) of a double pinion type, third and fourth planetary gear sets (PG3 and PG4) of a single pinion type, first to third clutches (CL1-CL3) engaging and disengaging predetermined rotating elements of the first to fourth planetary gear sets, and first and second brakes (BR1 and BR2) engaging and disengaging a second carrier (C2) and a first carrier (C1) from a transmission case (11). A gear ratio of the automatic transmission is 1 in a sixth gear.