A vehicle seat with a built-in cushion airbag device includes an inflator that produces gas by being activated; and a cushion airbag that is divided by a tether into a plurality of inflating portions including at least a rear-side inflating portion arranged on a seat lower side of a rear portion of a seat cushion, and a front-side inflating portion arranged to a seat front side of the rear-side inflating portion, and that inflates toward a seat upper side, with the front-side inflating portion becoming higher than the rear-side inflating portion, by the gas produced by the inflator being supplied.