Provided is an optical element that highly efficiently radiates light with high directivity at low etendue. The optical element includes a light emission layer (103) generating an exciton to emit light, a plasmon excitation layer (105) having a higher plasma frequency than a light emission frequency of the light emission layer (103), an output layer (107) converting light or a surface plasmon generated on an upper surface of the plasmon excitation layer (105) into light with a predetermined output angle to output the light, and a dielectric layer (102). In the optical element, a real part of an effective dielectric constant with respect to the surface plasmon is higher in an upper side portion than the plasmon excitation layer (105) than in a lower side portion than the plasmon excitation layer (105); a dielectric constant with respect to the light emission frequency of the light emission layer (103) is higher in a lowest layer than in a layer adjacent to a lower side of the plasmon excitation layer (105); and assuming that a radiation angle of a surface plasmon-derived highly directional radiation from the plasmon excitation layer (105) to the output layer (107) side is θout,spp and a radiation angle of an optical waveguide fundamental mode-derived highly directional radiation is θout,light, an absolute value of a difference between the θout,spp and the θout,light is less than 10 degrees.