It is a task to provide a fluorine gas supply system which can stably supply fluorine gas generated by a fluorine gas generation device to a semiconductor processing device in a large quantity and in a precise concentration. In the fluorine gas supply system, a mixed gas stored in a buffer tank is introduced into a gas introducing piping before the mixed gas is adjusted in the buffer tank to circulate the mixed gas and a monitoring device is disposed which measures a fluorine gas concentration within the mixed gas so that, in response to the obtained fluorine gas concentration, a flow quantity of inert gas supply source can be adjusted.