To provide a state monitoring system capable of registering a sensor to a monitor by simple operation.

A sensor 20 comprises a magnet 27 at sensor side detected by a reed SW60 at monitor side, a reed SW24 at a monitor side capable of detecting a magnet 61 at monitor side which has approached to a detectable zone, and a microcomputer at sensor side capable of transmitting an ID code when the magnet 61 at monitor side is detected by the reed SW24 at sensor side. A monitor 50 comprises the magnet 61 at monitor side, the reed SW60 at monitor side capable of detecting the magnet 27 at sensor side which approached to a detectable zone, and a microcomputer at monitor side capable of registering the ID code in the monitor 50 when the ID code is recognized to be capable of identifying the sensor 20 after the magnet 27 at sensor side is detected by the reed SW60 at monitor side.