A playing apparatus comprising: an optical system that irradiates a recording medium on which signals are recorded in both a land and a groove with light emitted from a light source to obtain signal light reflecting both recorded signals of the land and the groove, generates reference light from the light emitted from the light source, and generates a set of first signal light and reference light with a phase difference of almost 0 degree from overlapping light of the signal light and the reference light, a set of second signal light and reference light with a phase difference of almost 180 degrees from the same, a set of third signal light and reference light with a phase difference of almost 90 degrees from the same, and a set of fourth signal light and reference light with a phase difference of almost 270 degrees from the same; a light-receiving unit that receives the set of first signal light and reference light by a first light-receiving element, the set of second signal light and reference light by a second light-receiving element, the set of third signal light and reference light by a third light-receiving element, and the set of fourth signal light and reference light by a fourth light-receiving element; an arithmetic operation unit that calculates a first differential signal as 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 calculates a second differential signal as 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; a first FIR filter and a second FIR filter to which the first differential signal and the second differential signal are supplied, respectively; and an equalization error detection unit that is supplied with an addition signal in which output signals from the first and second FIR filters are added up to form an equalization error, wherein tap coefficients for the first and second FIR filters are controlled (57a, 57b) to minimize the equalization error. an optical system that irradiates a recording medium on which signals are recorded in both a land and a groove with light emitted from a light source to obtain signal light reflecting both recorded signals of the land and the groove, generates reference light from the light emitted from the light source, and generates a set of first signal light and reference light with a phase difference of almost 0 degree from overlapping light of the signal light and the reference light, a set of second signal light and reference light with a phase difference of almost 180 degrees from the same, a set of third signal light and reference light with a phase difference of almost 90 degrees from the same, and a set of fourth signal light and reference light with a phase difference of almost 270 degrees from the same; a light-receiving unit that receives the set of first signal light and reference light by a first light-receiving element, the set of second signal light and reference light by a second light-receiving element, the set of third signal light and reference light by a third light-receiving element, and the set of fourth signal light and reference light by a fourth light-receiving element; an arithmetic operation unit that calculates a first differential signal as 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 calculates a second differential signal as 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; a first FIR filter and a second FIR filter to which the first differential signal and the second differential signal are supplied, respectively; and an equalization error detection unit that is supplied with an addition signal in which output signals from the first and second FIR filters are added up to form an equalization error, wherein tap coefficients for the first and second FIR filters are controlled (57a, 57b) to minimize the equalization error.