An automatic transmission having small size and gear ratio for appropriately distributing eight forward speeds, capable of realizing transmission via all 8 shifts; rotation of input shaft is selectively transmitted to a first double pinion and a second double pinion, each element of the first and second double pinions are selectively fixed via first to forth brakes, in order to transmit rotation of the input shaft into a plurality of speeds to be transmitted to an output shaft. The first double pinion includes first and second sun gears, common planetary support capable of rotatably bearing long pinions and pinions, and common gear rings meshed with the first sun gear via the long pinion and pinion, and meshed with the second sun gear via the long pinion and pinion.