A two-wavelength antireflection film is constituted by a multi-layered film provided on a substrate so as to have antireflection characteristics for a wavelength .lambda..sub.1 and a wavelength .lambda..sub.2 different from the wavelength .lambda..sub.1. Each of the materials constituting the multi-layered film has a refractive index not exceeding 1.7 for a central wavelength .lambda..sub.0 which is defined by2/.lambda..sub.0 =1/.lambda..sub.1 +1/.lambda..sub.2.The materials constituting the multi-layered film are Al.sub.2 O.sub.3, SiO.sub.2 and MgF.sub.2, or Al.sub.2 O.sub.3 and MgF.sub.2. Each of plural films constituting the multi-layered film has an optical thickness equal to 1/4 of the central wavelength .lambda..sub.0.