An automatic transmission includes an input shaft, an output member, a first planetary gear system, a second planetary gear system, a third planetary gear system, a fourth planetary gear system, and an engagement mechanism. The input shaft is configured to be rotated with power of a driving source relative to the transmission case. The output member is to output rotation of the input shaft using multiple gear-shifting. The multiple gear-shifting is provided by setting at least three of first to third clutches and first to third brakes in a connection state.