A dielectric multilayer film is formed on one surface of a lens main body, a film including aluminum is formed on the other surface of the lens main body, the film including aluminum is immersed in hot water without immersing the dielectric multilayer film in the hot water, thereby changing the film including aluminum to a fine uneven structure film including an alumina hydrate as a main component, whereby a lens provided with antireflection functions on both surfaces is manufactured.