To provide a system which supplies nitrogen enriched air (NEA) produced by using bleed air as a supply source of the NEA to a fuel tank, and which can further improve the fuel consumption. The present invention employs an NEA supply system 10 that controls a supply in a flow control valve (FCV) 11 so as to obtain a supply flow rate Fs as a value obtained by adding a small margin flow rate Fm to a required amount Fn of nitrogen enriched air required to be supplied to a first fuel tank 15, in at least a part of a descent phase of an aircraft 100. Accordingly, explosion of the first fuel tank 15 can be prevented, and the fuel consumption of an engine 1 can be improved in the descent phase.