Error correction and/or detection device for product code block data

An error detection and correction device for product code block data comprising:

• reproducing means for reproducing from a recording medium input data composed of a plurality of product code blocks formed on a recording track of said recording medium, with each product code block comprising inner codes and outer codes for error correction annexed to said input data;
• inner code correction means for subjecting the reproduced input data to a first error correction by said inner codes for each of a plurality of inner code blocks and for outputting an error flag indicating that the inner code corrected data and error data uncorrected by the inner codes exist together;
• correction mode selection means for selecting a correction mode depending upon then umber of error flags output by said inner code correction means;
• outer code correction means for subjecting the inner code corrected data to second error correction by said outer codes for each of a plurality of outer code blocks depending upon the selected correction mode for outputting the outer code corrected data;
• first correlation detection means for checking the correlation between correction points of said outer code corrected data by said second error correction for each of said plurality of outer code blocks belonging to the same product code block and for determining whether the data in said product code block comprises unerased old data;
• and
• second correlation detection means for detecting, when the number of error flags in a given product code block is not less than a predetermined value, whether another product code block determined by said first correlation detection means to comprise unerased old data exists in the same recording track and, if the result of such detection is affirmative, determining that the data in said given product code block also comprises unerased old data.