Head-mounted display, head-mounted display linking system, and method for same

A display device comprising:

• a display;
• a camera;
• a communication module configured to perform communication connection with a mobile information terminal;
• and
• a processing circuit,
• wherein the display device stores an application software which is same as a software stored in the mobile information terminal,
• wherein the processing circuit is configured to:
• display an image taken by the camera on the display,
• display a display screen of the mobile information terminal on the display when the mobile information terminal is not included in the image,
• synchronize the application software stored in the display device with the software stored in the mobile information terminal,
• execute the synchronized application software,
• terminate displaying the display screen on the display in response to that the communication module receives a notification indicating a termination of the execution of the software stored in the mobile information terminal or a turning off of a power of the mobile information terminal.