A KVM switch includes: server units respectively connected to computers; user units respectively connected to input/output devices for transmitting signals to the computers and receiving signals from the computers; and a main unit that connects the server units and the user units. Each of the server units, user units and main unit is a communication unit and includes: a first part communicating with another communication unit to inform the above another communication unit of unit type information about the communication unit and receive unit type information about the above another communication unit therefrom; and a second part controlling communications with the above another communication unit on the basis of the unit type information acquired from the above another communication unit.