To provide an enciphering device which perform encoding and decoding through a simple procedure without requiring any special operation and is easily detached and preserved.

An enciphering device 1 has an interface part 11 attachable and detachable to an external connection bus 3 of a computer 2, a storage part 12, an encoding part 16 for encoding data and a decoding part 17 for decoding the encoded data and is constituted so as to be handled as an external storage device in hierarchical file configuration for the computer 2 when it is connected to the computer 2. Directories for encoding and decoding are provided and when a file is transferred to the directory for encoding, that file is encoded by the encoding part 16 and stored in the directory for encoding later but when a file is transferred to the directory for decoding, that file is decoded by the decoding part 17 and stored in the directory for decoding later.