An inflator securing structure for securing an inflator having substantially cylindrical shape to a retainer in an airbag system includes a fixed shaft having a substantially D-shaped cross section and formed at one end of the inflator along an axial direction of the inflator; and a locking structure forming a locking hole having a substantially D shape and formed in the retainer so that the locking hole is engaged with the fixed shaft. One of the fixed shaft and the locking hole has at least one groove, and other of the fixed shaft and the locking hole has at least one convex portion so as to engage with the groove.