A connection device connected to an image display unit that is head-mounted includes a connector to which an image signal is input; and a connector to which an image signal is input and which is capable of outputting sensor data. The connection device further includes a setting unit that sets a selection between the image signals; and an output control unit that selects the connector for outputting the image signal by a connection unit according to the setting. The setting unit sets the image signal to be output from the connection unit when the image signal is input.