Abstract: A number-of-compressors controlling system which has a simple configuration and can produce compressed air by immediately following the load used of the compressed air is provided. The number-of-compressors controlling system has a plurality of compressors (2), a receiver tank (3) in which compressed air is supplied from these compressors (2) and is fed to a compressed air utilization device, a pressure sensor (4) provided on the receiver tank (3), and a number-of-compressors controller (5) which changes the number of compressors being operated based on the detected pressure of the pressure sensor (4). A number-of-compressors decreasing pressure as a threshold value whether or not the number of compressors being operated is decreased by the number-of-compressors controller (5) is set to be lower as the number of compressors being operated is larger.