A polarizing filter has a laminate structure: wherein one to four layers of first dielectric thin films 1 and one to four layers of second dielectric thin films 2 are alternately laminated on a transparent flat substrate 10 to form the laminate structure, the layers of second dielectric thin films 2 having a refractive index lower than that of the first dielectric thin films 1 with respect to the wavelength of incident light; wherein one layer of the third dielectric thin film 3 having a refractive index intermediate between the refractive indices of the first and second dielectric thin films with respect to the wavelength of incident light is laminated on a surface of the laminate structure. In an optical device using the polarizing filter, the angle of incidence is set to be in a range of from 20 to 70 degrees.