<p>A content search device (1) calculates the number of valid encrypted contents as comparison objects contained in encrypted content databases (3, 121) and the number of valid decryption keys contained in decryption key databases (4, 21). The database having the smaller number is decided to be a reference database. By successively reading out entries contained in the reference database, a combination of an encrypted content and a corresponding decryption key is searched.</p>
