An optical pickup includes a wave plate on an optical path to be followed by every light beam emitted from three light sources (with wavelengths λ1, λ2 and λ3, respectively) both on their way toward an optical disc and back from the disc toward a photodetector. The wave plate has two layers with different retardations and different optic axis directions. The sum of the retardations of the first and second layers is defined to be approximately 5/4λ1, ¾λ2 and ½λ3 to the light beams with the wavelengths λ1, λ2 and λ3. Due to the difference in optic axis direction between the first and second layers, the linearly polarized light beams with the wavelengths λ1 and λ2 on their way toward the disc are transformed into circularly polarized light beams, which will be transformed again, on their way back from the disc, into linearly polarized light beams, of which the polarization direction is perpendicular to that of the light beams on their way toward the disc, thereby transmitting the light beam with the wavelength λ3 as a linearly polarized light beam both on its way toward, and back from, the disc.