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 .lamda.1 and a semiconductor laser chip that generates an optical beam having a wavelength of .lamda.2 are integrated into one chip or are arranged in proximity to each other. The diffraction grating has one grating period .LAMBDA. by which each of the optical beams having the wavelength .lamda.1 and the optical beam having the wavelength .lamda.2, 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.