The airbag apparatus includes an airbag having an exhaust hole for
discharging part of inflation gas, an open/close controller for
controlling opening and closing operations of the exhaust hole, and a
flap element releasably joined to the open/close controller and being
joined to a periphery of the exhaust hole in an outer side of the airbag
which periphery is in a side facing away from the open/close controller,
for opening and closing the exhaust hole. The apparatus further includes
an open/close means arranged in the periphery of the exhaust hole. Upon
airbag inflation, if the flap element is retained by the open/close
controller, the open/close means is held down at its outer side by the
flap element and keeps the exhaust hole closed. If the flap element is
released from the open/close controller, the open/close means opens by
the pressure of inflation gas to expand an opening area of the exhaust
hole.