Abstract: A server installed indoors determines whether or not an abnormality has occurred indoors. If the server determines that the abnormality has occurred, it causes an indoor display device having a display function to display a visually effective warning. A user is thereby promptly informed of the occurrence of the abnormality, and an appropriate countermeasure is swiftly taken. Upon detecting an indoor abnormality, the server decides on a display device for displaying the abnormality on the basis of a condition of a display device for displaying an abnormality and the circumstances of display devices connected to a network. Further, the server forms a screen used to report the abnormality depending on the contents thereof, and causes the display device, which has been decided on for the display of the abnormality, to display the screen.