A self standing center side airbag includes: an airbag cushion configured to be located at a side of an interior facing side of a seat back; a first through hole configured to penetrate through the airbag cushion and be located at a back with respect to a central line that bisects the airbag cushion in a front and back direction; a second through hole configured to penetrate through the airbag cushion and be located at a front with respect to the central line that bisects the airbag cushion in the front and back direction; and a tether configured to penetrate through the first through hole and the second through hole and have both ends fixed at the seat back side.