A pedestrian airbag device includes an airbag, which is housed folded in a vicinity of a rear end of a hood panel, and an inflator that supplies an inflating gas to the airbag. The airbag includes a vehicle body side wall portion disposed on a body side when inflation is completed, and a pedestrian side wall portion disposed opposing the vehicle body side wall portion. An internal pressure maintenance chamber is enclosed by a peripheral wall coupled to the vehicle body side wall portion and the pedestrian side wall portion, and is configured such that an inflating gas discharged from the inflator can flow into an interior via a general inflating portion in the airbag. A check valve mechanism that prevents a backflow to the general inflating portion side of the inflating gas that has flowed into the interior is disposed in the internal pressure maintenance chamber.