DECODING APPARATUS

PROBLEM TO BE SOLVED: To prevent a third person illicitly acquiring decoding key information from easily decoding a decoding program or encoded data by inputting the first decoding key information from outside a decoding apparatus and storing the second decoding key information into the decoding apparatus. SOLUTION: A mixing circuit 43 forms the decoding key information 18 by mixing the decoding key information 41 inputted from outside the decoding apparatus 12 and the decoding key information 42 stored in the decoding apparatus 12. An extraction circuit 26 extracts a decoding key from the decoding key information 18. The timing to extract the decoding key is controlled by a timing adjustment circuit 27. The decoding key extracted by this extraction circuit 26 is supplied through a conversion circuit 21 to a decoding circuit 22. The decoding circuit 22 decodes the data 16 encoded by using the decoding key or the encoded program 17. Consequently, the decoded data 16a or the decoded program 17a is outputted from the decoding circuit 22.