In an in-plane heterostructure photonic crystal in which vacancies 32 are periodically arranged in each of forbidden band zones 301, 302, with different cycle distances, a waveguide 33 is formed passing through all the forbidden band zones and point-like defects 341, 342, . . . are formed in each of the forbidden band zones. Since, of all light propagating through the waveguide from the light introduction/take-out section 36 and having the frequency 52 demultiplexed from the predetermined point-like defect, the wavelength of light passing through the predetermined point-like defect is not included in transmission bands 51 of the waveguide in the adjacent forbidden band zone, so that the light is reflected on the boundaries 351 and 352 between forbidden band zones and introduced into the point-like defect. Thereby, the demultiplexing efficiency of light is improved. The same applies to the multiplexing efficiency.