An objective lens for an optical information recording/reproducing optical system for an optical disc letting a laser beam impinge on a recording layer of the optical disc, and wherein a center wavelength λ (unit: nm) of the laser beam is in a range defined by a condition: 390≦λ≦420, a base material of the objective lens is made of resin, the resin has a glass transition temperature Tg and light transmissivity T (unit: %) per a path length of 3 mm at a wavelength of 406 nm defined by conditions: Tg≧115° C., 85≦T≦90, same antireflection films or different types of antireflection films are respectively formed on optical surfaces of the objective lens, and each of the antireflection films formed on the objective lens has a thickness of 100 nm or more in a vicinity of an optical axis of the objective lens.