An encryption device, a decryption device, an encryption method, and a decryption method effectively perform encryption and decryption by using a packet type judgment result. An encryption/decryption device includes a packet reception unit that acquires a packet, a first encryption engine that is formed by hardware and encrypts or decrypts a packet; and a second encryption engine that encrypts or decrypts a packet by using software. The encryption/decyption device also includes a head data identification unit that judges the real time feature of the acquired packet according to the header information on the acquired packet, and an encryption/decryption process judgment unit that decides the acquired packet encryption destination or decryption destination in accordance with the real time feature from the first encryption engine and the second encryption engine. Since it is possible to separate the encryption by hardware from encryption by software according to the packet real time feature, it is possible to effectively perform encryption and decryption.