An airbag apparatus for a vehicle includes: an airbag cushion including: a main panel; a main portion including a first sewn part joined to the main panel and a first chamber part, the main portion disposed in a side of a passenger when the airbag cushion is expanded by gas injected in the first sewn part; and an auxiliary portion including a second sewn part and a second chamber part, the auxiliary portion disposed in front of the passenger when the airbag cushion is expanded by gas injected in the second sewn part; and a connection member including a first end connected to the main portion of the airbag cushion and a second end fixed to the second sewn part of the auxiliary portion, the connection member being configured to guide the airbag cushion to be expanded in a shape of surrounding the passenger when the airbag cushion is expanded.