An optical device includes a first reflecting section, a second reflecting section, and a confining section. The first reflecting section is constituted of a thin-wire waveguide-type one-dimensional photonic crystal. The second reflecting section is constituted of a thin-wire waveguide-type one-dimensional photonic crystal of which a lattice constant differs from that of the first reflecting section. The confining section is sandwiched between the first reflecting section and the second reflecting section. A Fabry-Perot optical resonator is constituted by the first reflecting section, the confining section, and the second reflecting section.