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Abstract

A disk-like optical information recording medium in/from which information can be optically recorded/reproduced along a virtual track virtually defined in a spiral or concentric circular form on the recording medium is provided with a pair of wobbling pits provided for each predetermined data record unit and shifted in position in opposite senses of a radius direction with respect to a virtual track center and a group of at least two pits provided at specified positions in association with a leading one of the paired wobbling pits. The pit group forms together with the leading wobbling pit a mark following a predetermined modulation rule applied upon recording of information and changes between tracks adjacent to each other in the radius direction. An apparatus for recording/reproducing information in/from the recording medium includes an optical system for irradiating the recording medium with write-in light modulated in accordance with externally inputted recording information and irradiating the recording medium with reproduction light to detect light reflected therefrom, a detecting and decoding circuit inputted with a detection output of the optical system for detecting a position of the mark on the basis of a decoding method corresponding to the predetermined modulation rule, and a movement amount detecting circuit inputted with the mark position from the detecting and decoding circuit for detecting a change in relative position between a reproduced position on the recording medium and the optical system.

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