Abstract: Provided are an instantaneous interruption monitoring system and an instantaneous interruption monitoring program for a computer incorporating a non-real time operating system (OS). Measurement results acquired from optical time domain reflectometers (OTDR) can be continuously stored and the occurrence of an instantaneous interruption can be reported in real time. The system includes an instantaneous interruption monitoring program that determines the occurrence of an instantaneous interruption on a communication line, records instantaneous interruption information, and reports the occurrence of an instantaneous interruption.