A house monitoring system includes at least one sensor that detects a predetermined event, a master device that communicates with the sensor, and is connected to a fixed telephone network so as to perform calls to other fixed telephones, and a mobile phone terminal that includes a display/input unit, performs wireless communication with the master device by using a wireless router, and is connected to other mobile phones via a mobile phone network. When the sensor detects the predetermined event, the master device transmits information regarding the sensor having detected the predetermined event to the mobile phone terminal, and the mobile phone terminal displays the information regarding the sensor having detected the predetermined event transmitted from the master device on the display/input unit.