If content is transmitted/received through a digital signal bus, protection of copyright causes a problem because of no deterioration in quality. Accordingly, authentication is required. The quantity of information to be processed is, however, so large that a long time is required for authentication. Accordingly, both achievement of handling property as in conventional analog connection and protection of copyrighted content without user's awareness become an object. The foregoing object can be achieved by authentication which is executed, for management of copyright, among apparatuses connected to the digital signal bus when the apparatuses are powered on or connected to the digital signal bus or when an input terminal connected to the digital signal bus is selected. The object can be further achieved by an encryption key shared among these apparatuses.