Antireflection film and optical device

An antireflection film for a light beam having a wavelength of 400 nm to 800 nm inclusive, provided on a base material,

• comprising an optical two-layer structure composed of an intermediate layer to be provided on the base material and a low refractive index layer provided on a surface of the intermediate layer, wherein a reflectance against a light beam having a wavelength of 400 nm to 800 nm inclusive at an incident angle of 0° is 0.5% or less, and a reflectance against a light beam having a wavelength of 400 nm to 680 nm inclusive at an incident angle of 45° or less is 0.7% or less;
• wherein the low refractive index layer is a layer obtained by binding a hollow silica with a binder and the low refractive index layer has a refractive index n(1) of between 1.15 and 1.24 inclusive;
• wherein an optical film thickness of the low refractive index layer is between 100 nm to 180 nm inclusive;
• wherein an optical film thickness of the intermediate layer is between 100 nm to 180 nm inclusive;
• and
• a refractive index n(2) of the intermediate layer satisfies a relation in an expression (1) below assuming a refractive index of the base material n(sub):
• n(1)×√{square root over (n(sub))}×0.930≦n(2)≦n(1)×√{square root over (n(sub))}×0.985 (1).