To realize a dispersion-flat, athermal quartz-based optical waveguide which is manufactured at low temperatures and has a large refractive index difference.

On a silicon substrate 101, a pattern of a recessed part of desired optical waveguide width 103 is formed by photolithography. The width 103 without photoresist 102 is processed to form the recessed part 104. An inorganic coating glass film is applied and charged in the recessed part and cured at a temperature of 400°C. An excessive SOG film is removed by dry etching. An SiO2 film 106 as a core is formed on a clad layer 105 on the side wall and bottom in the recessed part by bias high-density plasma CVD. An SOG film is applied to a part as a clad layer and cured to form a quartz-based optical waveguide in buried structure. The surface of a deposited film is irradiated with plasma of NH3, N2, etc., to form a nitride layer or is sililated for damp-proof prevention, thereby forming a highly reliable quartz-based optical waveguide. Consequently, the quartz-based optical waveguide is realized at low temperatures and the refractive index difference is made as large as ≥3 %.