[Object] To increase the usability for users without decreasing the security level.[Solving Means] A personal computer (PC) 10 is connected to a television receiver (TV) 30 using an HDMI cable 1. When a video signal is transmitted from the PC 10 to the TV 30, a TMDS channel in the HDMI cable 1 is used. A high-speed data line that performs bi-directional communication using predetermined lines of the HDMI cable 1 (e.g., a reserve line and an HPD line) is provided. In PC 10, a firewall is set. When, for example, being connected to the PC 10, the TV 30 transmits a firewall turn-off command to the PC 10. Alternatively, when, for example, performing data transmission using the high-speed data line provided between the TV 30 and the PC 10, the TV 30 transmits a firewall turn-off command to the PC 10. The security level and connectivity can be maintained without troublesome setting performed by the user and, therefore, the usability for users can be increased.