The present invention provides a seat airbag device for a vehicle, the seat airbag device including an airbag cushion including a lateral chamber positioned at lateral sides of a passenger and configured to be deployed forward from a seatback of a vehicle, a front chamber configured to be deployed forward from an upper side of the seatback to surround the passenger, and an auxiliary chamber configured to be deployed from the front chamber toward a front side of the passenger so as to be positioned between the front chamber and the passenger, and a support tether extending from the seatback and connected to the airbag cushion to support the airbag cushion.