Patent ID: 7969847

Claim:
A disc apparatus comprising: a jitter-value detection unit configured to detect a jitter value based on a signal to be read from a medium; a defocus-value setting unit configured to set a defocus value for focusing an objective lens in the medium based on the jitter value; a defocus-value adjusting unit configured to: set the defocus value equal to a reference value; detect a reference jitter value when the defocus value is set equal to the reference value; and when the reference jitter value is greater than a predetermined jitter value: detect the jitter value every time the defocus value is changed stepwise within a predetermined range of the defocus value including the reference value of the defocus value, set the defocus value corresponding to a minimum jitter value of the detected jitter values as an optimum defocus value to be set for the defocus-value setting unit when a first value, which represents a difference between the minimum jitter value and a maximum jitter value of the detected jitter values, is greater than a second value, which represents a difference between the maximum jitter value and the predetermined jitter value, and set the reference value of the defocus value as the optimum defocus value to be set for the defocus-value setting unit when the first value is smaller than the second value; and a focus control unit configured to move the objective lens in a direction of an optical axis of the objective lens based on the optimum defocus value.