To improve quality of an audio signal and a video signal, without digitizing corridor lamps and a nurse call master unit, and without enhancing processing capability.

A controller 4 is provided with: a first IF 21 which converts an audio signal comprising analog data transmitted from a nurse call slave unit 1 into digital data, and converts an audio signal comprising digital data to be transmitted to the nurse call slave unit 1 into analog data; and a second IF 22 which converts analog data of a control signal and an audio signal, etc. transmitted from a nurse call master unit 3 into digital data, and converts digital data of a video signal and an audio signal, etc. to be transmitted to the nurse call master unit 3 into analog data. The controller 4, nurse call slave unit 1, and nurse call master unit 3 communicate with one another with the analog data, and the controller 4 is configured to internally perform signal processing with the digital data, thereby the controller 4 performs video signal processing and audio signal processing.