The present invention intends to extend the operating life of an air separation module (ASM) in a nitrogen enriched air (NEA) supply system by controlling the temperature of bleed air as a supply source of the NEA. The NEA supply system produces NEA that is enriched with nitrogen upon supply of source gas during a flight through an ascent phase, a cruising phase, and a descent phase, and supplies the NEA to a fuel tank, the system including: an air separation module that separates oxygen and nitrogen in the source gas; and a temperature regulation mechanism that regulates a temperature of the source gas supplied to the air separation module. In at least a part of a flight period through the ascent phase and the cruising phase, the temperature regulation mechanism regulates the temperature of the source gas to below a temperature of the source gas in the descent phase.