A seat cushion airbag device mountable to a vehicle seat that includes: a seat section including a seat cushion supported by a support section; and a blower duct having an outlet provided below the seat cushion so as to allow air-conditioning air to be ejected upward. The cushion airbag device includes an airbag, at least a part of which is inflated with an inflating fluid such that a seat surface of the seat section is bulged out. The airbag includes a folded portion. Before the airbag is inflated with the inflating fluid, the airbag is disposed at a position on a front side of the outlet while the folded portion is folded such that the outlet is exposed from the airbag. When the airbag is inflated, the folded portion is deployed so as to extend to a position on a rear side of the outlet.