Reproducing apparatus and reproducing method

A reproducing apparatus comprising:

• an optical system that irradiates a recording medium on which signals are each recorded on a land and a groove with a light beam emitted from a light source to obtain a signal light beam reflecting each of the recording signals of the land and the groove, generates a reference light beam from the light beam emitted from the light source, and generates a set of a first signal light beam and a reference light beam which give a phase difference of approximately 0° to a superimposed light beam obtained by superimposing the signal light beam and the reference light beam, a set of a second signal light beam and a second reference light beam which give a phase difference of approximately 180° to the superimposed light beam, a set of a third signal light beam and a third reference light beam which give a phase difference of approximately 90° to the superimposed light beam, and a set of a fourth signal light beam and a fourth reference light beam which give a phase difference of approximately 270° to the superimposed light beam;
• a light receiving unit that uses a first light receiving element to receive the set of the first light beam and the first reference light beam, a second light receiving element to receive the set of the second signal light beam and the second reference light beam, a third light receiving element to receive the set of the third signal light beam and the reference, and a fourth light receiving element to receive the set of the fourth signal light beam and the fourth reference light beam;
• a reproduction signal generating circuit that calculates a first difference signal a which is a difference between a first light receiving signal obtained by the first light receiving element and a second light receiving signal obtained by the second light receiving element, and a second difference signal b which is a difference between a third light receiving signal obtained by the third light receiving element and a fourth light receiving signal obtained by the fourth light receiving element, and
• uses the first difference signal a, the second difference signal b, a phase difference Ψ between a crosstalk component and an average phase of the signal light beam, and an optical path length difference θ between the signal light beam and the reference light beam to carry out an arithmetic operation of
• a·sin(Ψ−θ(t))−b·cos(Ψ−θ(t))
• to obtain a reproduction signal;
• and
• a phase extraction circuit that obtains a successive change amount Δθ of θ and updates θ with the successive variation Δθ.