An inflator is located inside an airbag of airbag device for supplying inflation gas. The inflator includes a substantially cylindrical body for generating inflation gas, and a substantially tubular retainer made of sheet metal to be mounted around the body for holding the body by fastening a fastening portion. The retainer includes mounting bolts for mounting the airbag to a predetermined mounting position. The retainer includes a fastening portion, a first support portion and a second support portion which are arranged in order along axial direction of the body to abut against a circumference of the body. The fastening portion and the second support portion are located in a substantially opposite area from the first support portion in the circumference of the body based on a center of a cross section of the body taken perpendicularly to the axial direction of the body as the retainer holds the body.