A radio bus system, a radio communication apparatus and a registration communication method which can ensure a minimum level of secrecy even when radio is used during an authentication information registration procedure. A hub station and each terminal comprises a mode switching control circuit (10) for switching between two modes, one being a registration mode to be used for the transmission and reception of registration data, and the other being a normal mode to be used for the transmission and reception of general data other than the registration data, a scrambler (transmitter means) (22) for transmitting data after providing the data with predetermined data processing corresponding to the mode switched to, and a descrambler (receiver means) (27) for performing on received data a predetermined restoration process corresponding to the mode switched to. Restoration of the received data is enabled only when the mode on the transmitting end and that on the receiving end correspond with each other.