A data copying system of the present invention includes a data copying apparatus for copying data recorded on a first recording medium to a second recording medium. The data copying apparatus includes: a data read section for reading out the data from the first recording medium; a data modification control section for controlling modification of the data in accordance with modification control information, the modification control information being provided for controlling the modification of the data; and a data write section for writing an output of the data modification control section to the second recording medium. The modification control information includes a copying permission flag indicating whether the copying of the data permitted, a quality control flag for controlling a quality of modified data which is obtained by modifying the data, and a billing control flag for controlling billing for the copying of the data. The data modification control section determines whether billing is required for the copying of the data in accordance with the billing control flag. When the billing is required, the data modification control section controls the modification of the data in accordance with the copying permission flag and the quality control flag, after confirming that the billing has been done by the billing apparatus. When the billing is not required, the data modification control section controls the modification of the data in accordance with the copying permission flag and the quality control flag, without confirming that the billing has been done by the billing apparatus.