An ultraviolet reflecting mirror comprises a substrate, a high reflection factor film provided on the substrate and having a film thickness of at least 250 .ANG. and reflecting a light beam by the surface thereof, and a group of dielectric material layers comprising one or more sets of two layers of low refractive index film and high refractive index film provided on the high reflection factor film. The low refractive index film is provided on the high reflection factor film. The optical film thickness of the high refractive index film and the low refractive index film is approximately 1/4(2n-1).lambda., where n is a natural number and .lambda. is the design wavelength and 150nm.ltoreq..lambda..ltoreq.300nm. The film thickness of at least one of the high refractive index film and the low refractive index film is 3.lambda./4.