<P>PROBLEM TO BE SOLVED: To detect tracking error signals with less offset, even when an optical storage medium, having two information recording planes and being recordable, is used. <P>SOLUTION: A diffraction means receives a beam projected from a light source and generates a plurality of diffracted light beams of 0-th order and first-order or higher. A convergence means receives a plurality of beams from the diffraction means and converging the beams on the optical storage medium. A beam-splitting means receives a plurality of beams reflected by the optical storage medium and splits them, a photodetection means receives a plurality of beams and outputs a signal that corresponds to the amount of light received. The diffraction means is provided with grating patterns in which phases of a center part and its both sides are different each other. Directions and periods of grating pattern, provided at the both side of the center part, are the same, and phases are reversed by 180 degrees each other. <P>COPYRIGHT: (C)2007,JPO&INPIT 
OPTICAL PICKUP HEAD DEVICE AND INFORMATION RECORDING AND REPRODUCING APPARATUS