An optical device includes a light-guiding plate that guides light in a plane parallel to an emission surface that emits light, and a sensor for detecting an object located on an emission surface side using light that passes through a back surface opposite to the emission surface and through the emission surface. The light-guiding plate has light convergence portions that receive light guided by the light-guiding plate and each have optical surfaces that cause light to be emitted from the emission surface in directions in which the light substantially converges at or scatters from one convergence point or one convergence line in a space, and the convergence points or the convergence lines for the light convergence portions are different from each other, and an image is formed in the space on the emission surface side by a collection of the convergence points or the convergence lines.