In a vehicle seat, a gas generating device of a side airbag apparatus is attached to the inside of an outer side frame in a seat-width direction. When a seated occupant is a three-dimensional mannequin of AM50, a portion of the gas generating device overlaps a back pan of the three-dimensional mannequin as viewed in a seat front-rear direction. Here, in a plan section of a seat back in a range in which the gas generating device is positioned in a seat up-down direction, when an imaginary line overlapping a section of the back pan is moved back toward a seat rear side until the imaginary line comes into contact with a side spring portion of a seat back spring, the gas generating device is positioned rearward of a moved-back imaginary line in the seat front-rear direction and outward of the moved-back imaginary line in the seat-width direction.