SIDE AIRBAG DEVICE AND AIRBAG FOLDING METHOD

The side airbag device includes an airbag in a folded state, including a pair of sheets provided facing each other, and an inflator including a supply port for supplying gas and configured to supply gas into the airbag. The airbag, with the pair of sheets deployed, includes a first portion including one end of the sheets in a first direction, a second portion including the other end, a third portion positioned between the first portion and the second portion, and a fourth portion positioned between the first portion and the third portion. The airbag is folded into a first state with the first portion and the fourth portion positioned between a pair of sheet parts corresponding to a part of the pair of sheets and included in the third portion, and further folded into a second state with a part of the pair of sheet parts arranged to sandwich the first portion and the fourth portion, folded with an accordion fold in a second direction perpendicular to the first direction. The supply port is arranged between another part of the pair of sheet parts.