A base station used in a mobile communications system which uses orthogonal frequency division multiplexing (OFDM) for downlink is disclosed. The base station includes: a unit which provides a reference signal; a unit which multiplexes a control signal and the reference signal, and generates a transmit symbol; and a unit which inverse Fourier transforms the transmit symbol and wirelessly transmits the transformed transmit symbol, wherein a first sequence including a random code sequence and a second sequence belonging to an orthogonal-code sequence group are multiplied with the reference signal, mutually different ones of the orthogonal code sequences are used in the respective multiple sectors belonging to the same cell, and different ones of the random code sequences are used in the respective two or more cells.