In a monitoring system, a master device stores setting information indicating a detection area of a target detected by a sensor in a storage unit, and transmits the setting information to a camera (a baby monitoring camera) having a sensor built thereinto or correlated with a sensor so as to set a detection parameter including the detection area therein. When a predetermined state set by the detection parameter is detected inside the detection area by the camera, a master device transmits detection notification information to a smartphone, and the smartphone displays a detection information screen based on the detection notification information transmitted from the master device on a display/input unit.