To provide a monitoring system in which it is necessary only to provide a common detecting part at a monitoring side regardless of the classification of plural tag sensors 7 to be used, and it is possible to reduce manufacturing costs.

This system is provided with plural tag sensors 7 respectively arranged at plural parts to be monitored with different monitoring classifications which detect the states of the parts to be monitored by resistance values, plural resistance value judging parts 6 connected with the plural tag sensors 7 which judge the resistance values detected by the plural tag sensors 7, and output judgment signals, and monitoring part main body 1 which selectively and successively receives the judgment signals outputted by the plural resistance value judging parts 6, and operates the display of an abnormal state when the received judgment signal is abnormal. The plural tag sensors 7 are selected so that the normal ranges of the resistance values can be made almost coincident.