A reproducing apparatus comprising: an optical system configured to irradiate 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, to generate a reference light beam from the light beam emitted from the light source, and to generate 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 configured to use 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 (31a, 31b) configured to calculate 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 to use 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; characterized by a phase extraction circuit configured to obtain a successive change amount Δθt of θt according to the following expression: wherein η is a learning coefficient, F is a function, and to update θt to θt+1 = θt + Δθt, and the reproduction signal generating circuit (31a, 31b) is configured to use the updated θt+1 to obtain the reproduction signal. an optical system configured to irradiate 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, to generate a reference light beam from the light beam emitted from the light source, and to generate 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 configured to use 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 (31a, 31b) configured to calculate 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 to use 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 to update θt to θt+1 = θt + Δθt, and the reproduction signal generating circuit (31a, 31b) is configured to use the updated θt+1 to obtain the reproduction signal.