An optical device (100) includes a first substrate (10) and a second substrate (20), and an optical layer (30) interposed therebetween. The first substrate includes a first electrode (11) and a second electrode (12), and the second substrate includes a third electrode (21). The optical layer contains a medium (31) and anisotropically-shaped particles (32) whose alignment direction changes in accordance with the direction of an electric field applied to the optical layer. The first electrode and the second electrode, which are interdigitated electrodes, are disposed so that their respective branches (11a, 12a) mesh with one another via a predetermined interspace. The relationships w1