To provide a state monitoring system for a building which has further improved convenience while suppressing lowering of a security level.

The state monitoring system 1 has a sensor device 2 which detects a state of a monitoring object and a monitoring device 3 which notifies the state of the monitoring object based on an input signal from the registered sensor device 2. The monitoring device 3 has a monitoring side microcomputer 33 which is switched to a registration mode in which the sensor device 2 can be registered, a monitoring mode in which the state of the monitoring object is notified based on the input signal from the registered sensor device 2 and an alarm mode in which an alarm is raised when the state of the monitoring object changes. The monitoring side microcomputer 33 registers the sensor device 2 as a special monitoring object to be monitored in a mode different from a normal monitoring mode for immediately raising the alarm when the state of the monitoring object changes in the alarm mode, when the first to third password input switches 38a-38c are operated in registration of the sensor device 2.