Provided is a cryptographic device performing encryption or decryption on input data, and more particularly, a cryptographic device having a session memory bus for communicating with a session memory. The cryptographic device includes: an external session memory for storing cryptographic information on each session; a cryptographic processor for encrypting or decrypting input data using the cryptographic information; an external session memory bus connected to the external session memory and the cryptographic processor; and a Central Processing Unit (CPU) for transferring and receiving data to and from the external session memory via the cryptographic processor. The separate session memory buses allow the cryptographic processor to access a session memory without being disturbed by another device, thereby improving the entire performance of the cryptographic device.