An optical device includes: a first reflective surface disposed to reflect, to a substantially arc-shaped first region around a first axis, at least a portion of first light incident along the first axis and having a light distribution characteristic with an optical axis parallel to the first axis, the first reflective surface including a plurality of reflective arc surfaces separated in a direction along the first axis; a second reflective surface and a third reflective surface intersecting each other on the first axis and disposed such that the first reflective surface is located between the second reflective surface and the third reflective surface; and a light-transmissive emission surface adapted to refract at least a portion of light reflected by the plurality of reflective arc surfaces to emit the light around the first axis, the emission surface having periodic irregularities in a cross section in the direction along the first axis.