To provide a cemented optical element which prevents reflection of finite light in a plurality of wavelength bands over a wide range, and a cementing method.

A polarizing beam splitter (PBS) 14 includes a first prism 31, a second prism 32, a polarizing split film 29, an antireflection film 33, and an adhesive 34. The first and second prisms 31 and 32 are made of transparent materials and are cemented to each other by the adhesive having a refractive index less than those of the first and second prisms 31 and 32. The polarizing split film 29 is provided on a surface of the first prism 31. The antireflection film 33 is provided on a surface of the second prism 32 to which the first prism 31 is cemented, has a refractive index distribution in which a refractive index decreases from the second prism 32 side to the adhesive 34 side, and prevents the reflection of light between the second prism 32 and the adhesive 34.