In a gas generator of the invention, a closure member is disposed so as to
be connected to an outer circumferential wall side along a
circumferential edge thereof in a housing and to close an outlet port
which is formed in a ceiling wall of the housing. Thin breakable portions
adapted to be broken when a squib is activated are formed in the closure
member so as to extend substantially radially from a center of the
closure member in a rectilinear fashion. When the squib 19 is activated,
the breakable portions are broken, whereby portions of the closure member
11 which lie between the breakable portions are individually made to be
opened radially. A stopper portion is formed on a closure member side
surface of the ceiling wall such that the opened door portions are
brought into abutment therewith so that the opening angles of the door
portions become less than 90.degree. while ensuring an angle at which
combustion gas is allowed to flow out.