There is provided an intercom system which realizes high-quality image display and communication with low cost.In the intercom system, front door slave unit 300 having an attached camera and master unit 400 are connected to each other through a two-wire cable, and communication between front door slave unit 300 and master unit 400 is performed with transmission and reception of an image signal. Front door slave unit 300 packetizes a control signal, an image signal, and a sound signal of front door slave unit 300, generates an uplink signal, and transmits the generated uplink signal to master unit 400. Master unit 400 packetizes a control signal and a sound signal of master unit 400, generates a downlink signal, and transmits the generated downlink signal to front door slave unit 300. Front door slave unit 300 and master unit 400 perform transmission of the uplink signal and transmission of the downlink signal in a manner of time division duplex using the two-wire cable.