An automatic transmission excelling in transmission efficiency than the prior art is provided. The automatic transmission is equipped with an input shaft 2 and an output shaft 3 and a plurality of planetary gear mechanisms 5, 6. Any one element Sa of a plurality of the planetary gear mechanisms 5, 6 is coupled to the input shaft 2. One element Ca is coupled to the output shaft 3 via the first gear row G1. One element Rb is connected to the output shaft 3 via a second gear row G2 having a gear ratio different from that of the first gear row G1. Five or more engagement mechanisms C1 through C3, B1, B2 for coupling each element Ra and Cb, each element Sb, Cb with the input shaft 2, and each element Sb, Cb with the transmission case 1 releasably.