A vehicle seat with a side airbag device that is stowed inside it and secured to a seat side frame , comprising: an airbag that restrains an occupant when expanded and deployed; an inflator that supplies expansion gas to the airbag ; and a bracket that retains the airbag and the inflator and is connected to the side frame , wherein the airbag includes a pre-push chamber with the inflator stowed inside and deploys primarily on the occupant side (inner side) of the side frame , and a main chamber that is connected to the pre-push chamber and deploys primarily toward the front of the side frame , the bracket includes a first surface that faces the direction of travel of the vehicle (forward) and a second surface that faces the center side of the seat (inner side) in the width direction of the vehicle, and at least the main chamber is arranged on top of the first surface of the bracket when the airbag is in a folded and/or rolled stowed state, wherein in a stowed state, the pre-push chamber of the airbag is arranged on top of the second surface of the bracket wherein the pre-push chamber of the airbag deploys towards the occupant side with the second surface of the bracket as a reaction surface, characterized in that the main chamber is partitioned into a forward chamber and a rear chamber ; a reference line (L0) is set along the rear edge of the rear chamber when viewed from the side in the vehicle width direction; and the rear chamber is configured such that at least one of a shoulder protecting region that protects the shoulder area, and a waist protecting region that protects the waist area, respectively of an occupant seated in the seat, reaches near the front end of the forward chamber . an airbag that restrains an occupant when expanded and deployed; an inflator that supplies expansion gas to the airbag ; and a bracket that retains the airbag and the inflator and is connected to the side frame , wherein the airbag includes a pre-push chamber with the inflator stowed inside and deploys primarily on the occupant side (inner side) of the side frame , and a main chamber that is connected to the pre-push chamber and deploys primarily toward the front of the side frame , the bracket includes a first surface that faces the direction of travel of the vehicle (forward) and a second surface that faces the center side of the seat (inner side) in the width direction of the vehicle, and at least the main chamber is arranged on top of the first surface of the bracket when the airbag is in a folded and/or rolled stowed state, wherein in a stowed state, the pre-push chamber of the airbag is arranged on top of the second surface of the bracket wherein the pre-push chamber of the airbag deploys towards the occupant side with the second surface of the bracket as a reaction surface, a reference line (L0) is set along the rear edge of the rear chamber when viewed from the side in the vehicle width direction; and the rear chamber is configured such that at least one of a shoulder protecting region that protects the shoulder area, and a waist protecting region that protects the waist area, respectively of an occupant seated in the seat, reaches near the front end of the forward chamber . <EOS>