GAS GENERATOR

The present invention provides a gas generator, including a cylindrical housing having therein an ignition device chamber and a pressurized gas chamber, a closing member in a circular shape having a fragile portion provided on one surface and closing between the chambers, a piston being disposed inside the ignition device chamber and having a base plate and a rod that extends in the axial direction from one surface of the base plate to abut against or face the closing member, the fragile portion being a groove formed with a curve extending from a start point A on Y1 to an end point E through a first intermediate point B on Y2, a second intermediate point C on Y1, and a third intermediate point D on Y2, where Y1 and Y2 are two straight lines drawn to be orthogonal to each other and to pass through a crossing point X2 on one surface of the closing member, the groove formed so that distances from the crossing point X2 to the respective points satisfy the following relationship: the distance to the start point A < the distance to the first intermediate point B < the distance to the second intermediate point C < the distance to the third intermediate point D < the distance to the end point E, and that the end point E is a point (E1) crossing Y1 after passing through the third intermediate point D on Y2, a point (E2) closer to the third intermediate point D than to the crossing point, or a point (E3) that has passed by E1, the rod being not to come in contact with the start point A but pushing at a position close to the groove between the start point A and the first intermediate point B, and thereby the closing member being ruptured along the groove from the start point A to the end point E.