In a vehicle seat comprising a seat cushion and a seatback, the seatback comprises a seatback frame including a right and a left side member extending vertically, a side airbag unit attached to one of the side members, a flexible seatback pad provided with a pad side slit to permit an airbag to be deployed opposite to the side airbag unit, a skin member having a skin side slit in a part thereof corresponding to the pad side slit, and a retaining sheet connected to a part of a back side of the seatback pad opposing the side member, and to the side member so as to fixedly secure a position of the seatback pad relative to the side member.