A format-preserving encryption device for encrypting an input d-digit plain text and for outputting a cipher text in a same data format as the plain text, d being an integer of three or more, the encryption device comprising: unit block tweakable encryption means for encrypting a specific one digit of the plain text by using respective numerical values of remaining two or more digits excluding the specific one digit of the plain text and an external tweak that is input concurrently with the plain text; block permutation means for permutating the encrypted one specific digit of the plain text and the remaining two or more digits of the plain text, per digit, based on a predetermined rule and supplying a d-digit output to the unit block tweakable encryption means ; and encryption counter update means for causing processing by the unit block tweakable encryption means and block permutation means to repeat for a predetermined number of times, wherein the unit block tweakable encryption means includes: an AES encryptor adapted to encrypt a numerical value that concatenates the remaining two or more digits excluding the specific one digit of the plain text and the external tweak using a prestored encryption key and outputs an output value of a specific number of bits; a temporary encryption key generator adapted to generate a temporary encryption key using an output value of the AES encryptor ; and a block encryptor adapted to encrypt the specific one digit of the plain text utilizing the temporary encryption key, characterized in that the block encryptor is adapted to encrypt the specific one digit of the plain text by permutation using Knuth Shuffle. unit block tweakable encryption means for encrypting a specific one digit of the plain text by using respective numerical values of remaining two or more digits excluding the specific one digit of the plain text and an external tweak that is input concurrently with the plain text; block permutation means for permutating the encrypted one specific digit of the plain text and the remaining two or more digits of the plain text, per digit, based on a predetermined rule and supplying a d-digit output to the unit block tweakable encryption means ; and encryption counter update means for causing processing by the unit block tweakable encryption means and block permutation means to repeat for a predetermined number of times, wherein the unit block tweakable encryption means includes: an AES encryptor adapted to encrypt a numerical value that concatenates the remaining two or more digits excluding the specific one digit of the plain text and the external tweak using a prestored encryption key and outputs an output value of a specific number of bits; a temporary encryption key generator adapted to generate a temporary encryption key using an output value of the AES encryptor ; and a block encryptor adapted to encrypt the specific one digit of the plain text utilizing the temporary encryption key, characterized in that the block encryptor is adapted to encrypt the specific one digit of the plain text by permutation using Knuth Shuffle. an AES encryptor adapted to encrypt a numerical value that concatenates the remaining two or more digits excluding the specific one digit of the plain text and the external tweak using a prestored encryption key and outputs an output value of a specific number of bits; a temporary encryption key generator adapted to generate a temporary encryption key using an output value of the AES encryptor ; and a block encryptor adapted to encrypt the specific one digit of the plain text utilizing the temporary encryption key, characterized in that the block encryptor is adapted to encrypt the specific one digit of the plain text by permutation using Knuth Shuffle. <EOS>