A vehicle seat provided with a side airbag device, comprising: a seatback frame that is provided with a pair of left and right side frames and that configures a seatback framework member; a side airbag device that is installed at a seat width direction outer-side of the one of the side frames disposed facing a vehicle body side portion, and that inflates and deploys a side airbag towards a seat front-side in the event of a side-on collision; a seat back board made from resin, that is disposed at a seatback back face side and that is fixed to the pair of left and right side frames; and a seatback pad that is disposed at a front face side of the seat back board, with a seat width direction outer-side side portion of the seatback pad disposed at the seat width direction outer-side of the side airbag device; characterized by: an upright wall portion that is provided on a seat width direction outer-side of a side portion of the seat back board and is provided integral with the side portion of the seat back board, and that extends in a seat front-rear direction and a seat up-down direction along a seat width direction outer-side side face of the side airbag that is in a folded state inside the side portion of the seatback pad, the upright wall portion restricting expansion of the side airbag towards the seat width direction outer-side during inflation and deployment of the side airbag towards the seat front side; and wherein a case portion including a side wall portion that serves as the upright wall portion and doubles as an airbag case that at least houses the side airbag in a folded state, and is provided with a bottom wall portion that is integrally formed to the seat back board, that extends in a direction intersecting with the upright wall portion and that is connected to a lower end portion of the upright wall portion. a seatback frame that is provided with a pair of left and right side frames and that configures a seatback framework member; a side airbag device that is installed at a seat width direction outer-side of the one of the side frames disposed facing a vehicle body side portion, and that inflates and deploys a side airbag towards a seat front-side in the event of a side-on collision; a seat back board made from resin, that is disposed at a seatback back face side and that is fixed to the pair of left and right side frames; and a seatback pad that is disposed at a front face side of the seat back board, with a seat width direction outer-side side portion of the seatback pad disposed at the seat width direction outer-side of the side airbag device; characterized by: an upright wall portion that is provided on a seat width direction outer-side of a side portion of the seat back board and is provided integral with the side portion of the seat back board, and that extends in a seat front-rear direction and a seat up-down direction along a seat width direction outer-side side face of the side airbag that is in a folded state inside the side portion of the seatback pad, the upright wall portion restricting expansion of the side airbag towards the seat width direction outer-side during inflation and deployment of the side airbag towards the seat front side; and wherein a case portion including a side wall portion that serves as the upright wall portion and doubles as an airbag case that at least houses the side airbag in a folded state, and is provided with a bottom wall portion that is integrally formed to the seat back board, that extends in a direction intersecting with the upright wall portion and that is connected to a lower end portion of the upright wall portion. an upright wall portion that is provided on a seat width direction outer-side of a side portion of the seat back board and is provided integral with the side portion of the seat back board, and that extends in a seat front-rear direction and a seat up-down direction along a seat width direction outer-side side face of the side airbag that is in a folded state inside the side portion of the seatback pad, the upright wall portion restricting expansion of the side airbag towards the seat width direction outer-side during inflation and deployment of the side airbag towards the seat front side; and wherein a case portion including a side wall portion that serves as the upright wall portion and doubles as an airbag case that at least houses the side airbag in a folded state, and is provided with a bottom wall portion that is integrally formed to the seat back board, that extends in a direction intersecting with the upright wall portion and that is connected to a lower end portion of the upright wall portion.