An optical pick-up apparatus includes: a semiconductor laser light source that generates an optical beam; a diffraction grating that divides the optical beam into a main beam and side beams; an optical element that guides the main beam and the side beams that are generated by the diffraction grating onto an optical information medium; and a photodetector that detects a signal from reflected light reflected from the optical information medium. The semiconductor laser light source is configured with a 2-wavelength semiconductor laser device in which a semiconductor laser chip that generates an optical beam having a wavelength of λ1 and a semiconductor laser chip that generates an optical beam having a wavelength of λ2 are integrated into one chip or are arranged in proximity to each other. The diffraction grating has one grating period Λ by which each of the optical beams having the wavelength λ1 and the optical beam having the wavelength λ2, which are generated by the 2-wavelength semiconductor laser device, is divided into a main beam and side beams. The apparatus is applicable to two kinds of optical information media having different track pitches.