[Subject] To provide a format-preserving encryption device and the like that enables efficient and secure encryption/decryption while maintaining the data format.[Solution] An encryption device 10 includes: an unit block tweakable encryption module 101 that encrypts a specific digit of a plain text by using numerical values of remaining respective digits excluding the specific digit of the plain text and an external tweak that is input concurrently with the plain text; a block permutation module 102 that permutates respective digits including the encrypted specific digit of the plain text per digit based on a predetermined rule; and a counter update module 103 that causes processing by the unit block tweakable encryption unit and the block permutation unit to repeat for a predetermined number of times. A decryption device 20 performs the reverse processing to the encryption device 10.