An optical device includes a light-emitting device and a sensor device (a light receiving element). The light-emitting device includes a substrate, a plurality of light-emitting elements, and a plurality of light-transmitting units. The substrate has a first surface and a second surface. The second surface is opposite the first surface. The plurality of light-emitting elements are located on the first surface side of the substrate. Each of the plurality of light-transmitting units is located between light-emitting elements adjacent to each other. The light-emitting device has light-transmitting properties by the plurality of light-transmitting units. Light from the plurality of light-emitting elements is emitted mainly from the second surface of the substrate. The amount of light leakage from light emitted from each light-emitting element and leaked toward the outside of the first surface of the substrate is suppressed.