Abstract: A seat structure equipped with a side impact air bag apparatus in which, when an external force is applied to a side of a vehicle, an air bag apparatus mounted to a side portion of a seat back frame is operated, a sewn portion of seat surface layers is ruptured, and thereafter, an air bag body is unfolded, includes an air bag case, the air bag case having a lid which is opened due to the unfolding of the air bag body. When the lid is opened, a seat pad which is disposed further toward the front of the vehicle than the lid is compressed by the lid toward the inner side of a seat back in the transverse direction of the seat back.