In a data recording apparatus which sequentially records recording data on a magnetic tape (T), when a plurality of continuously recorded data files F(i) are rewritten into new data files F(I) having smaller data quantities, recording areas which remain without being rewritten into the new data files F(I) are rewritten into unrecorded areas NR containing no data. Further, when rewriting into new data files G(I) which have larger data quantities, reserve areas SP are provided, in which data has not been previously recorded, and overflow data is written into the reserve areas SP at the time of rewriting. Furthermore, when rewriting into a new data file H(I) having a larger quantity, in a case where the data file H(i+1) following the rewritten data file H(i) is not needed, the recording areas of the unnecessary data file H(i+1) which are not rewritten, are rewritten into a new data file H(I+1) having no data, or are rewritten into the above mentioned reserve areas SP belonging to a newly rewritten data file A(I).