In a monitoring system, a master device that is connected to a fixed telephone network so as to perform calls to other fixed telephones sets a power supply device to an operation mode in a case where a mobile phone terminal is located within a wireless communication range of the master device, and sets the power supply device to an operation stop mode in a case where the mobile phone terminal is not located within the wireless communication range of the master device. A power supply device is connected to an electric apparatus disposed in a house, supplies power to the electric apparatus in a case where the operation mode is set by the master device, and does not supply power to the electric apparatus in a case where the operation stop mode is set by the master device.