A gas generator for an air bag, includes: a housing having a gas discharging hole; an ignition unit activated upon an impact, the ignition unit including at least one igniter and at least one transfer charge, the transfer charge being a mixture of a transfer charge power and a gas generating agent molded article, and the gas generating agent molded article generates a gas of at least 1.2 moles/100 g; and a combustion chamber accommodating a gas generating agent which is ignited and burnt to generate a combustion gas.