An optical plate having an exit pupil array or a lens array aligned at a predetermined pitch is disposed at the front of a display. A test pattern is supplied to the display to light a pixel corresponding to the predetermined pitch. A first optical element transmits a light from an inspection position of the optical plate. A second optical element coaxially disposed on the first optical element, focuses the light from the first optical element. An image from the light focused at the second optical element is obtained. A three-dimensional position at the inspection position of the optical plate relative to the display or a predetermined period of the optical plate is calculated from a position and a period of luminance distribution of the image, and a distance between the optical plate and the first optical element. Whether the three-dimensional position or the predetermined period is within a threshold is inspected.