To easily judge which of deterioration etc., due to secular change etc., of equipment and poorer eyesight etc., of an observer causes a video display defect of a head mount display.

A test chart is displayed by a video display means of the head mount display, a test chart which can be compared with the test chart is provided on the reverse surface of a battery lid of a control unit, and the observer compares both the test charts with each other while putting on the head mount display.