Optical pickup device, optical disc device, and diffraction grating

The invention relates to an optical pickup device, an optical disc device and a diffraction grating. The optical pickup device and an optical recording/reproduction device are provided that can suppress a tracking error signal offset generated in the boundary between an unrecorded area and a recorded area. A three-beam diffraction grating is divided into two areas. A division line that divides the diffraction grating into two areas has a step in the direction almost vertical to a groove period structure, and the part of the division line in the step has a staircase shape. The phase differencein the groove period structures between one area and the other area, separated by the division line, is about 180 degrees.