To provide a state monitoring device for a building capable of further improving convenience.

A monitoring device 3 has a monitor side microcomputer 33 for switching to a registering mode capable of registering a sensor device 2, a monitoring mode of notifying a state of a monitoring object on the basis of an input signal from the registered sensor device 2, and a warning mode of issuing a warning when the state of the monitoring object changes. The monitor side microcomputer 33 in the registering mode classifies the sensor device 2 of an object into groups corresponding to operation when either of first to third identification code input switches 38a to 38c is operated over a long time. The monitor side microcomputer 33 switches, when mode switching operation is performed with a group selected, the mode with only the sensor device 2 belonging to the group as the object.