According to an embodiment, a recording/reproducing apparatus includes a diffraction grating and a light-receiving element. The diffraction grating divides return light from the guide layer in accordance with areas. The areas include a first area and a second area that does not overlap the first area. The light-receiving element includes (i) a first detecting cell group which receives a zero-order beam to which astigmatism is imparted, (ii) a second detecting cell group which receives at least one of a positive and negative first-order beam, which passes the first area and made astigmatic, and (iii) a third detecting cell group which receives at least one of a positive and negative first-order beam, which passes the second area and made astigmatic.

A reproducing device (100) includes (i) an optical pickup (6) for irradiating, with reproduction light, an optical disk (1) which is a super-resolution medium, (ii) an RF signal processing circuit (9) for converting, into a reproduction signal, light which reflected off optical disk (1), (iii) an i-MLSE detecting section (141) for evaluating quality of the reproduction signal, and (iv) a spherical aberration correcting section (142) for correcting a spherical aberration by using a result of evaluation of the quality of the reproduction signal.

There are provided an optical disk and an optical disk recording method which are capable of stable data reading in a case where a recording linear density is increased. According to an optical disk of the present disclosure, a run-in pattern recorded in a groove track and a run-in pattern recorded in a land track are made different patterns so that no great change is caused in the amplitude of an acquired signal due to interference between adjacent recording patterns, and thus, data may be stably read.

An optical-information recording/reproducing apparatus of the present invention is capable of carrying out position detection of a reproduction image even if reproduction image data with incomplete alignment marks (markers) is obtained. A relative correlation value is calculated from a first correlation value retained by a first correlation-value retaining unit and a second correlation value retained by a second correlation-value retaining unit, and pass/fail of a position detection result of the marker is judged according to the relative correlation value. The pass/fail of the position detection result is judged by mutually comparing the detection positions of the markers judged as passes by the relative correlation-value judgement, the positions of the markers judged as fail by the relative correlation-value judgement or the mutual position judgement is complemented, and the position of two-dimensional data is detected based on the pass-judged markers and the complemented markers.

This recording/reproducing apparatus that records or reproduces information by radiating light to a recording medium is provided with: a medium rotating unit that rotates the recording medium; a moving unit having a movable unit that is capable of moving within a predetermined plane; a rotation angle detecting unit that detects a rotating angle of the recording medium using an angle detection mark that is provided on the recording medium; a position detecting unit that detects a position of the recording medium using an eccentricity detection mark that is provided on the recording medium; and a member for fixing the rotation angle detecting unit and the position detecting unit. With respect to the member, the movable unit relatively moves within a plane substantially parallel to the recording surface of the recording medium, and the medium rotating unit is fixed to the movable unit.