1. A head mounted display comprising: a display unit which is configured to project an image light having intensity corresponding to image information on an eye of a user thus allowing the user to visually recognize an image corresponding to the image light while allowing an external light to pass therethrough; an imaging unit which is configured to image a predetermined range including at least a range where the image is displayed out of a field-of-view range of the user; an image forming unit which is configured, when an image is superposed on a background image derived from the external light and visually recognized by the user, to form a background cancelling image which constitutes the image having reference background brightnesses which are fixed brightnesses within a predetermined frame period for respective three primary colors and cancels the background image based on an imaged image imaged by the imaging unit; an image processing unit which is configured to combine the background cancelling image with an original image corresponding to original image information by aligning the background cancelling image and the original image with each other in terms of display position and size; and a display control unit which is configured to perform a control by which an image to which the background cancelling image is combined is displayed by the display unit.