A connection device to which a PC and a head-mounted image display unit that includes a right display unit and a left display unit configured to display an image are connected, the connection device including a control unit configured to control the right display unit and the left display unit to enable execution of functions including a display function of displaying an image input from the PC and a display stop function of stopping display, wherein the control unit activates the image display unit in a display mode based on a display condition when power supply to the connection device is started, and the display mode includes at least a first display mode in which the image is displayed on the right display unit and the left display unit and the display stop function is disabled.