Head mounted display

A head mounted display (HMD) according to the present invention is capable of controlling various functions on the basis of movement of a main body thereof. In addition, in order to control the various functions, the HMD can set a moving area where the main body is to be moved, and display alert information when the main body deviates from the moving area. More specifically, an HMD according to one embodiment of the present invention comprises: a main body configured to be worn on a user's head; a display unit, installed on one area of the main body, for outputting display screen information; and a control unit for controlling the display unit in a way that, in a taken image including an image of a preset object, the screen information is changed on the basis of detection of a deformation in the image, wherein the control unit controls the display unit in a way that, if at least one portion of the image is not detected in the taken image, alert information related to the movement of the main body is displayed together on the screen information.