The airbag apparatus includes an airbag housed in a folded state and an inflator for supplying inflation gas to the airbag. The inflator includes a first gas supply region and a second gas supply region respectively supplying inflation gas into the airbag under control of a control device. The first gas supply region is operable independently and in advance of the second gas supply region. The substance quantity of inflation gas supplied to the airbag by the first gas supply region per unit time at the time the first gas supply region operates independently and in advance of the second gas supply region is less than the substance quantity of inflation gas supplied to the airbag by the second gas supply region per unit time.