A gas generator comprising: a housing (10, 20) having a cylindrical circumferential wall portion (12, 22) provided with a plurality of gas discharge openings and having one end portion and the other end portion in an axial direction of the circumferential wall portion (12, 22) closed; a gas generating agent arranged in an accommodation space located in the housing (10, 20); an igniter assembled to the housing (10, 20), for burning the gas generating agent; and a sealing tape which closes the plurality of gas discharge openings, each of the plurality of gas discharge openings being opened as a portion of the sealing tape which closes each of the plurality of gas discharge openings is cleaved with increase in pressure in the accommodation space as a result of burning of the gas generating agent, the plurality of gas discharge openings including gas discharge openings set to be different from one another in opening pressure expressed as F×t×C/S so as to be opened stepwise with increase in pressure in the accommodation space as a result of burning of the gas generating agent, where F represents shear strength of the sealing tape, t represents a thickness of the portion of the sealing tape which closes each of the plurality of gas discharge openings, C represents a circumferential length of each of the plurality of gas discharge openings, and S represents an opening area of each of the plurality of gas discharge openings, characterized in that a condition of T ≤ 1.8 [mm] and SA ≥ 60 [mm 2] being satisfied, where T represents a thickness of a portion of the housing (10, 20) which defines the accommodation space and SA represents a total opening area of the plurality of gas discharge openings, and at least one of the plurality of gas discharge openings being in a shape of an elongated hole different in opening width in directions orthogonal to each other. a housing (10, 20) having a cylindrical circumferential wall portion (12, 22) provided with a plurality of gas discharge openings and having one end portion and the other end portion in an axial direction of the circumferential wall portion (12, 22) closed; a gas generating agent arranged in an accommodation space located in the housing (10, 20); an igniter assembled to the housing (10, 20), for burning the gas generating agent; and a sealing tape which closes the plurality of gas discharge openings, each of the plurality of gas discharge openings being opened as a portion of the sealing tape which closes each of the plurality of gas discharge openings is cleaved with increase in pressure in the accommodation space as a result of burning of the gas generating agent, the plurality of gas discharge openings including gas discharge openings set to be different from one another in opening pressure expressed as F×t×C/S so as to be opened stepwise with increase in pressure in the accommodation space as a result of burning of the gas generating agent, where F represents shear strength of the sealing tape, t represents a thickness of the portion of the sealing tape which closes each of the plurality of gas discharge openings, C represents a circumferential length of each of the plurality of gas discharge openings, and S represents an opening area of each of the plurality of gas discharge openings, characterized in that a condition of T ≤ 1.8 [mm] and SA ≥ 60 [mm 2] being satisfied, where T represents a thickness of a portion of the housing (10, 20) which defines the accommodation space and SA represents a total opening area of the plurality of gas discharge openings, and at least one of the plurality of gas discharge openings being in a shape of an elongated hole different in opening width in directions orthogonal to each other.