To provide an inflator capable of easily holding a gas supply body on a retainer.

This inflator 20 includes the generally cylindrical gas supply body 21 for discharging a gas for expansion and the retainer 26 having a bolt 33 for holding the gas supply body and attaching and fixing the gas supply body to a mounting portion. The retainer 26 includes a cylindrical body 27 formed in a generally cylindrical shape and having the bolt 33, and a linear spring piece 41 assembled in the cylindrical body 27. The spring piece 41 includes a locking rod part 42 which projects into the cylindrical body in the direction generally parallel to the direction RV perpendicular to the axis of the cylindrical body, which is restricted to move along the axial direction RD of the cylindrical body, and which is deformable and restorable along the direction apart from the axis RC of the cylindrical body. The gas supply body 21 is restricted to move along the axial direction GD by fitting the locking rod part 42 to the fitting groove 24 of the outer peripheral surface 21a thereof, and held on the retainer 26 by restricting the movement thereof in the direction GV perpendicular to the axis by the inner peripheral surface 27d of the cylindrical body.