In an airbag folding method, an airbag is folded so as to provide a rolled-up shape thereon using a core member including air suction holes from which air can be sucked in. Firstly, the core member is disposed on part of the spread airbag that is to be rolled up at a location which corresponds to a center of a rolled-up shape when formed, and following this, the core member is rotated so as to wind up the airbag around the core member to thereby form a spiral shape while air is being sucked in from the air suction holes so that the airbag is drawn to be secured to an outer circumferential surface of the core member. Thereafter, a rolled-up shape is formed on the airbag by removing the core member.