Optical disks and reproduction thereof

When an optical disk having a plurality of recording layers is loaded, in which layer-number data is recorded on the recording layer nearest to the signal reading plane and layer I.D. data is recorded on each recording layer, a pickup reads the data recorded on each recording layer. A focus error signal is produced by a quartered detector by using return light from the pickup. A focus search drive circuit generates a focus drive signal. When focalization on a desired recording layer is established during focus search by the focus search drive circuit, the focus search drive circuit is stopped.