Patent ID: 8208353

Claim:
A disk apparatus for information recording/reproducing of an optical disk having two or more information planes, comprising: a radiation unit for irradiating a laser beam toward said optical disk; a motion unit for moving a focal point of said laser beam along a focus direction of said optical disk; a photodetector unit for detecting light returned from said optical disk; a focus error signal generator unit for generating a focus error signal from a signal obtained by said photodetector unit; a pull-in error signal generator unit for generating a total sum signal of signals obtained by said photodetector unit; and a focus control unit for controlling a focal point of said laser beam to move from one information plane to another information plane of said optical disk in accordance with said focus error signal; wherein said focus control unit controls to detect whether said laser beam is in-focus on said information plane, in accordance with gradients of said focus error signal and said pull-in error signal; and wherein said focus control unit controls in such a manner that a focal position of said information plane is not detected in accordance with said focus error signal, if a sign of the gradient of said focus error signal changes and a sign of the gradient of said pull-in error signal does not change, in a range where a focus of said laser beam is moved from one information plane to another adjacent information plane, whereas a focal position of said information plane is detected in accordance with said focus error signal, if a sign of the gradient of said focus error signal changes and a sign of the gradient of said pull-in error signal changes.