In a monitoring system, a master device transmits predetermined sound source list data to a mobile phone terminal in response to a first operation on a display/input unit. The mobile phone terminal displays the predetermined sound source list data transmitted from the master device on the display/input unit, and transmits information regarding a selected sound source to the master device in response to an operation of selecting one sound source from the sound source list data. When the information regarding the sound source is received from the mobile phone terminal, the master device outputs selection audio data corresponding to the information regarding the selected sound source from a speaker of a monitoring camera.