An objective lens according to the present invention is provided for use in an optical pickup apparatus at least reproducing and/or recording information using a light flux with a wavelength .lamda.1 emitted by a first light source for a first optical disc and reproducing and/or recording information using a light flux with a wavelength .lamda.2 emitted by a second light source for a second optical disc. The objective lens includes a diffractive structure formed on the at least one optical surface of the objective lens. The light fluxes with the wavelengths .lamda.1 and .lamda.2 enter the objective lens, an optical system magnifications m1 and m2 of the objective lens respectively for the light fluxes with wavelengths .lamda.1 and .lamda.2 have different signs and values from each other, and the diffractive structure has a positive diffractive action.