A gas generator includes a plurality of gas discharge openings arranged in a circumferential wall portion along a circumferential direction as not overlapping with each other. The plurality of gas discharge openings consist of one group or two or more groups of first gas discharge openings, one group or two or more groups of second discharge openings, and one group or two or more groups of third gas discharge openings. The gas discharge openings included in each of the groups of first to third gas discharge openings are set to be opened at an identical opening pressure. The second gas discharge openings are higher in opening pressure than the first gas discharge openings and lower in opening pressure than the third gas discharge openings. The gas discharge openings included in each group of gas discharge openings are evenly arranged in rotation symmetry at an angle not greater than 120°.