A selectively deployable airbag apparatus for vehicles includes: an impact detection sensor; a seat belt sensor; a first inflator and a second inflator; an airbag supplied with gas emitted from the first inflator and the second inflator and having a base chamber and a chest chamber separated from each other by a partition with at least one inner vent hole such that the base chamber and the chest chamber fluidly communicate with each other; and a controller receiving signals from the impact detection sensor and the seat belt sensor and operating the airbag to deploy, and determining whether to deploy the chest chamber or not based on whether the passenger has fastened the seat belt or not and an impact force.