PURPOSE: To obtain a remote monitoring system capable of executing transmission among plural remote monitoring devices by driving any one of slave machines as a master machine even when an original master machine runs down and switching the using right of a communication line for sending information to a receiving equipment.

CONSTITUTION: In the remote monitoring system connecting the remote monitoring devices 8a to 8n to the same communication line, setting up one of the devices 8a to 8n as a master machine and others as slave machines and switching the using right of the line by means of a system for inquiring the slave machines by a broadcasting format while supplying current from the master machine and allowing respective slave machines to respond in the order of slave machine setting numbers, a result that inquiring signals corresponding to the number of slave machines has not been received is recognized when the master machine runs down, any one of the slave machines acts as a master machine by supplying current.