To monitor each vacuum valve unit and a vacuum station at real time by a control department, to immediately find a place at the time when abnormality occurs in a vacuum valve and a vacuum sewage pipe and to speedily restore it.

A sensor to detect an inside ate and a terminal instrument 3 are set on a vacuum valve unit 1, the terminal instrument 3 is connected to a cable 5 laid along a vacuum sewage pipe 4, and one end of the cable 5 is connected to monitor systems 6, 7, 8 set on a vacuum station 9. States of the vacuum valve unit 1 and pumps are monitored by the monitor systems, after a vacuum valve is opened and sewage water is carried, a value of a pressure sensor is monitored for a constant period of time after a point of time when the vacuum valve works to close, and while the value of the pressure sensor is continuously lowered, it is judged as abnormality of the vacuum valve and it is alarmed and displayed to the vacuum station 9.