Provided is a cryptographic device for fast session switching, and more particularly, a cryptographic device using a block cipher algorithm and capable of rapidly performing session switching. The cryptographic device includes: a block cipher algorithm executer for performing encryption or decryption on input data using an initialization vector and a round key corresponding to a current session; an initialization vector manager for storing an initialization vector input from outside of the cryptographic device and an initialization vector received from the block cipher algorithm executer, and providing the initialization vector corresponding to the current session to the block cipher algorithm executer; and a session round key generator for storing a session key input from outside of the cryptographic device, generating the round key based on a session key corresponding to the current session, and providing the round key to the block cipher algorithm executer. The device has a structure capable of performing minimum operation to store and manage an initialization vector and a session key, and thus can minimize delay time caused by session switching.