A manufacturing method is provided for a light modulation device that improves utilization efficiency of light. After forming a first reflective layer using a metallic material such as Pt or the like, on a substrate, a light modulating film is formed using an electro-optic material in which refractive index changes in accordance with an applied electrical field. After that, planarization is carried out so that irregularities on an upper surface of the light modulating film are less than or equal to 1/100 of the wavelength of light incident on the light modulation device. A transparent electrode is then formed using ITO, ZnO, or the like, on the light modulating film, and a second reflective layer including a dielectric multilayer is formed.