The present disclosure relates to a block cipher apparatus and method for real-time data transmission and the block cipher apparatus according to an exemplary embodiment of the present disclosure includes: a block encryption unit which selects a key in accordance with an order of keys having different lengths to encrypt each plaintext block and generate a ciphertext block; and a message authentication unit which generates a message authentication code using a key selected at the time of encrypting a current plaintext block which is encrypted in the block encryption unit and a previous message authentication code generated by a plaintext block before the current plaintext block.