In a vehicular seat, a side airbag module and a side support bladder are arranged inside a shell frame that constitutes a skeleton of a seat back. A base bracket of a support body is disposed between the side support bladder and the side airbag module. This base bracket is supported by the shell frame. The base bracket supports the side support bladder from outside in a seat width direction at the time of inflation of the side support bladder, and is rotated inward in the seat width direction around a hinge together with the side support bladder due to an inflation pressure of a side airbag at the time of inflation and deployment of the side airbag.