in an optical disk having various information recorded thereon on a frame - by - frame basis , each of the frames being organized in a predetermined format comprising a main channel where data are recorded and a subcode providing additional information including recorded positions of the data , table - of - contents or toc information for the data recorded in the main channel is contained in the main channel of the optical disk . when a subcode block representing a single unity of information is formed of a plurality of the subcodes belonging to 98 efm frames , the table - of - contents information is recorded in the main channels of the 98 frames in such a manner that every piece of information needed as the table - of - contents information is fully accommodated in a predetermined data block made up of the data of the main channels belonging to the 98 frames . thus , there can be provided an optical disk and optical disk reproduction system which permit high - speed readout of the toc information .