A monitoring system that monitors a steam-using facility includes a temperature sensor that is a trap temperature sensor configured to detect a temperature of a steam trap provided in a steam discharge unit and/or a steam temperature sensor configured to detect a temperature of steam flowing into the steam trap and a pressure sensor configured to detect a pressure of steam flowing into the steam trap. The monitoring system determines that there is an occurrence of an abnormality or a sign of the abnormality in the steam trap when (i) a temperature detection value obtained by the temperature sensor and/or statistical temperature data obtained by performing statistical processing on the temperature detection value deviates from a predetermined criterion thereof and (ii) a pressure detection value obtained by the pressure sensor and/or statistical pressure data obtained by performing statistical processing on the pressure detection value deviates from a predetermined criterion thereof.