An objective lens, for an optical information read/write device that performs read/write operations on each of a plurality of optical discs using a corresponding one of three laser beams having first, second, and third wavelengths .lamda.1, .lamda.2, and .lamda.3 (nm) satisfying a relationship .lamda.1<.lamda.2<.lamda.3, respectively, includes a phase shift structure having a plurality of ring-shaped refractive surface zones into which at least one surface of the objective lens is concentrically divided. The objective lens is made of material with an Abbe number .nu.d satisfying a condition 40.ltoreq..nu.d.ltoreq.80. The phase shift structure has a step between each couple of the adjacent refractive surface zones that gives an optical path difference to an incident laser beam, so that a condition 2N+1.00<|.DELTA.OPD/.lamda.1|<2N+1.30 is satisfied, where .DELTA.OPD represents the optical path difference (nm) that the step gives to the laser beam with the first wavelength, and N represents a non-negative integer.