A reproduction signal output from a reproduction device is output via a relay device to two or more display devices including an excellent display device that is used by being mounted on the head of a user.A connection monitoring circuit in a front end box 40 monitors both a +5V signal of a source appliance that is HDMI-connected to an HDMI input unit 501, and an HPD signal of a sink appliance that is HDMI-connected to a second output unit 503. Then, only when an HPD signal emitted by the HDMI sink appliance is detected together with a +5V signal emitted by the HDIM source appliance does the connection monitoring circuit in the front end box 40 enables a repeater function with respect to the HDMI sink appliance.