| 摘要 |
A focus servo control is performed by changing a condition of a focus servo loop from an open condition to a close condition in correspondence with a level of a reflection light signal, which is obtained as a reflection light of a light beam reflected from an information record medium is detected by a light receiving element such as an optical pickup. A focus servo controlling apparatus is provided with a disturbance level detecting device such as a servo control circuit for detecting a level of a disturbance light signal, which is obtained as a disturbance light other than the reflection light is received by the light receiving element; and a controlling device such as a system controller for setting a level, which is larger than the level of the disturbance light signal detected by the disturbance level detecting device, as a threshold level and for changing the condition of the focus servo loop from the open condition to the close condition on the basis of a timing when the level of the reflection light signal becomes equal to or larger than the set threshold level.
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