Side airbag device-installed vehicle seat

A side airbag device-installed vehicle seat comprising:

• a side frame disposed within a side section of a seatback;
• a side airbag disposed within the side section of the seatback, the side airbag being configured to receive gas supplied from an inflator so as to inflate and deploy alongside a seated occupant, the side airbag including:
• a side airbag body configured to inflate and deploy between the seated occupant and a vehicle body side section, and
• an inner bag configured to inflate between the side frame and the seated occupant, and when inflated, the inner bag being configured to push the seated occupant toward an inner side in a vehicle width direction;
• a front side cover forming a part of a cover of the seatback and facing the inner bag, the front side cover being configured to be interposed between the inner bag and the seated occupant when the inner bag is inflated;
• and
• a first low extendibility member configured to stretch less readily than the front side cover, the first low extendibility member having a sheet shape and being bound to an entire back face of a lower section of the front side cover.