An optical element has a dichroic film held between transparent materials which transmits one of first light in a wavelength range of 390 to 425 nm and second light in a wavelength range of 630 to 820 nm and reflects the other light, and a first, a second, a third and a fourth surfaces. In the optical element, a first anti-reflection film for preventing reflection of the first light is formed on the first surface, a second anti-reflection film for preventing reflection of the second light is formed on the second surface, and a third anti-reflection film for preventing the reflection of the first and the second light is formed on the third surface from which the incident light of the first surface and the second surface is emitted. In the third anti-reflection film, reflectance of the second light is larger than that of the first light.