Number-of-compressors controlling system

The invention provides a number-of-compressors controlling system which can rapidly trace usage load of compressed air to produce the compressed air by adopting a simple structure. The system comprises multiple compressors (2), a receiver tank (3), a pressure sensor (4) arranged in the receiver tank (3), and a number-of-compressors controlling machine (5) which changes the number of the running compressors (2) based on detected pressure of the pressure sensor (4), wherein the compressed air is supplied by the compressors (2) and delivered to a compressed air-using device by the compressors (2). Pressure for reducing the number of the compressors is a boundary value for indicating whether the number of the running compressors should be reduced by using the number-of-compressors controllingmachine (5), and the pressure for reducing the number of the compressors is set to be reducing as the number of the running compressors increase.