To correctly discriminate whether the present track is a land track or a groove track.

When an FMC signal detecting circuit 28 generates a fine clock mark signal on the basis of reflected light from an optical disk 50, a variable gain amplifier 30 amplifies this fine clock mark signal. The amplified fine clock mark signal is compared with threshold values by comprators 42a, 42b, and based on the outputs of the comparators 42a, 42b, a land/groove discrimination circuit 44 discriminates whether the present track is a land track or a groove track. Tracking is controlled according to the result of this discrimination. On the other hand, a DSP 40 fetches a peak level of the amplified fine clock mark signal, and adjusts slice levels to be set for the comparators 42a, 42b on the basis of this peak level.