An optical element which includes an optical block having a cavity part formed on an optical path and an inclined face formed in an internal face of the cavity part at a prescribed inclining angle with respect to a traveling direction of light. Multilayer films of the same structure are formed at least on the internal face of the cavity part and on an interface between a light incident end and/or emission end of the optical block and outside. The multilayer film formed on the incline face in the internal face of the cavity part has at least a wavelength selecting function for light to be used.