PURPOSE: To secure the sufficient capacity of a gas generating agent and make the laminated height always the same by forming plural grooves, reaching the outer periphery from the inner periphery of a through hole, on both faces of the gas generating agent.

CONSTITUTION: A gas generating agent 13 is of ring plate shape with a through hole 15 formed at the center, and plural groove parts 37 reaching the outer periphery from the inner periphery of the through hole 15 are formed at one face 13a and the other face 13b. The groove parts 37 are formed with the angle difference of 30 between one face 13a and the other face 13b. Upon ignition, a flame sets on fire in the through hole 15 and simultaneously enters into contact parts in the gas generating agent 13 from the groove parts 37 so as to make the ignitability of the gas generating agent 13 extremely desirable. In the case of forming protrusions at the gas generating agent 13, the capacity of the gas generating agent 13 is reduced due to the formation of relatively large space parts, but with the groove parts 37 formed, sufficient capacity is secured since only the spaces corresponding to the groove parts 37 are formed.