An optical pickup device has a semiconductor laser emitting light which is in turn branched via a diffraction grating into at least three beams of light including a main beam and two sub beams which are in turn condensed via an objective lens on an optical disk at a guide groove and reflected by the optical disk to provide three reflections of light which are in turn received by detectors, each divided into two regions, respectively, to generate a tracking error signal. The diffraction grating is divided into three regions including a first region, a second region and a third region located intermediate therebetween, each having a periodical structure out of phase, the periodical structure having grating grooves in a direction determined depending on the phase of the second region to incline relative to a direction perpendicular to the guide groove of the optical disk.