Data recorder and method for recording data

PROBLEM TO BE SOLVED: To avoid nonconformities where a tracking servo deviates in a prescribed block area, when an optical disk is played back by a ROM drive or the like in the case that shift processing is applied to the prescribed block area of the optical disk, by preventing the prescribed block area from turning into an unrecorded portion. SOLUTION: When a normal write clock is no longer generated correctly during writing data in a block area A, writing of data is stopped (Fig. 11 (a)) and shift processing is applied to this block area. Then, data are written in the block area A by using a reference clock based on a signalling frequency from a quartz oscillator. Data are recorded so as to span the next block area A+1 (Fig. 11 (b)), thereby the area following the block area A is prevented from constituting the unrecorded portion caused by the irregular rotation of the optical disk or the like. Data are recorded on the block area A+1 (Fig. 11 (c)) by using a usual write clock. The shift processing is applied also to the block area A+1.