An optical attenuator (8) has a substrate (glass substrate) (1) and an optical attenuation film (2) that attenuates an input light with a predetermined optical attenuation factor, and the optical attenuation film (2) is disposed on a light input face (3) of the substrate (1). An angle defined by the light input face (3) and the light output face (4) of the substrate (1) is set to 0.15° to 0.5°. A protective film (5) for preventing the deterioration of the optical attenuation film (2) is formed on a surface of the optical attenuation film (2).