PURPOSE: To attain dissidence of a character string at high speed by detecting the dissidence of the character string through the comparison of hash values.

CONSTITUTION: A character string data I functioning as a reference is inputted to input data. The data I is applied with hash processing with the 1st hash processing section 3 and the hash value obtained as the result is set to a section 5-2 of a character string data register 5. On the other hand, a character string data IIcompared with the identity is inputted to the input register 2, the data II is applied with has processing by the 2nd hash processing section 4 and the hash value obtained is set to a section 6-2 of a character string data register 6. The set hash value to sections 5-2, 6-2 is compared by the comparator 7 and when the hash value is different, the comparator 7 outputs 0 and an inverter 8 outputs logical 1. Thus, when the hash value is effective and dissident with each other, a dissident signal is outputted from an AND gate 9.