PURPOSE: To improve the processing capacity of the reactive holding monitoring for plural devices performing the distributed processings.

CONSTITUTION: A holding time statistical processor 1 receives the notification of the holding (using)time of the communication line from a network connection device 2, calculates the suspected reactive holding time by the statistical processing and indicates it as the monitoring interval to a reactive holding suspected line detection device 3. The reactive holding suspected line detection device 3 selects a line group 7 from the plural line groups by the indicated monitoring interval and collects the line states by a line state collection device 4 two times. When the communication line is holding state two times, the monitoring request is performed for a reactive holding suspected line monitoring device 5 and a monitoring line group 7 is updated. The reactive holding suspected line monitoring device 5 performs the monitoring of the suspected line by a line monitoring device 6. When it is judged as the reactive holding, the device 5 requests a network connection device 2 to release the line.