An optical information recording-and-reproducing unit includes a diffraction section provided with a reflected optical beam reflected on a storage medium. The diffraction section has at least first and second areas, and from each of the first and second areas, a +1-order diffraction light and a -1-order diffraction light are produced. The unit further includes first and second optical detection sections respectively provided with one of a pair of +1-order diffraction lights and a pair of -1-order diffraction lights produced from the first and second areas of the diffraction section. The unit still further includes a first circuit section for generating a tracking error signal based on output signals of the first and second optical detection sections. In the unit, the light provided to the first optical detection section forms a first spot in a far-field state before convergence, and the light provided to the second optical detection section forms a second spot in a far-field state after convergence.