A circuit for descrambling a packet transmitted from and received in a communication device, includes (a) a plurality of descramblers each receiving words obtained by developing the packet in parallel and descrambling data in the words to be descrambled, each of the descramblers being associated with a combination of addresses of the data in the words, (b) a padding number detector which counts a padding number of a final word among the words, based on data indicative of a packet length, which data is included in the packet, and (c) a data selector which selects one of outputs transmitted from the descramblers in association with the combination, to thereby receive data obtained by descrambling the words, from the thus selected descrambler. A circuit for scrambling a packet includes similar components.