Optical disc device, optical disc rotation position detection method, and optical disc having rotation reference mark formed as width changing in radial direction

An optical disc device, comprising:

• an optical disc rotation drive unit configured to rotate an optical disc provided with a rotation reference mark having optical reflectivity and being formed on an upper portion of a first surface of the optical disc;
• an optical sensor configured to detect the rotation reference mark by emitting sensing light to a region of the optical disc where the rotation reference mark is located;
• and
• a control circuit configured to control the optical disc rotation drive unit and the optical sensor,
• the rotation reference mark being formed into a shape having a width changing in a radial direction of the optical disc,
• the control circuit being configured to extract a detection signal of the rotation reference mark as a pulse waveform from an output signal of the optical sensor with the optical disc being rotated, calculate a shifted amount of an actual detection position from a targeted detection position in accordance with the pulse waveform, and specify a rotation reference position, which is a reference position in a rotation direction, of the optical disc in accordance with the shifted amount.