A transmission signal generator produces N transmission pulses for every transmission period from N (N: an integer of 2 or more) kinds of transmission code sequences and (N×M) (M: an integer of 2 or more) kinds of orthogonal code sequences, the transmission pulses being obtained by multiplying transmission codes of the N kinds of transmission code sequences, with selected N orthogonal codes of the (N×M) kinds of orthogonal code sequences. In one transmission period, a radio transmitter converts the N transmission pulses to high-frequency signals, and transmits the signals through a transmission antenna. The (N×M) kinds of orthogonal code sequences are code sequences which satisfy a predetermined mathematical expression in M transmission periods.