A detachable head mounted display (HMD) device includes a display unit configured to display a user interface, a detached sensor unit configured to detect whether the HMD device has been affixed to eye-glasses, a sensor unit configured to detect an input signal generated when the eye-glasses to which the HMD device is affixed are touched, and a controller configured to control the display unit, the detached sensor unit, and the sensor unit. The controller is further configured to acquire identification information of the eye-glasses if the HMD device detects that the HMD device is affixed to the eye-glasses, to acquire a look up table related to the identification information, to acquire a control input related to the input signal from the look up table in response to the detected input signal, and to control the user interface to perform a function corresponding to the control input.