An ignition element mounting capacitor having an ignition element mounted on a capacitor, includes therein a first capacitor section and a second capacitor section, and first external terminal electrodes electrically connected to the first capacitor section and second external terminal electrodes electrically connected to the second capacitor section. The first capacitor section has a capacity for igniting ignition powder, and the second capacitor section has a function for removing noise which affects external circuits. Further, provided on the surface of the capacitor are third external terminal electrodes electrically connected to the ignition element. In this manner, the invention provides a squib enabling its size to be miniaturized and its quality to be improved, while keeping a high productivity, and hence provides a header assembly and a ignition element mounting capacitor as components of the squib and further provides a gas generator having such a squib installed therein for an air bag and a gas generator having the squib for a seat belt pretensioner.