The present invention relates to an encryption key generating method ensuring resistance to collusion attacks and achieving reduction in a key length of encryption keys corresponding to respective hierarchies of each scalability. In the encryption key generating method, an encryption key (K2,2) corresponding to data in the lowest hierarchies of hierarchical scalabilities (R, L) is divided as a master key by the number of hierarchies in scalability (R). Key element matrices (M1-M3) generated with respective split keys (eR2, eR1, eR3) are assigned operation data successively obtained by repeating a hash operation with a one-way hash function, so as to maintain hierarchical nature of scalability (L). Partial keys (K1,1-K2,2) corresponding to respective hierarchies of the scalabilities (R, L) are generated by combining key elements coordinately consistent among the key element matrices (M1-M3).