A transmitter in a mobile communication system code-multiplexes transmission symbols together with spreading codes, performs inverse Fourier transform and transmits the result from multiple transmit antennas. A receiver in the mobile communication system performs Fourier transform on signals received at multiple receive antennas, extracts signal components of individual subcarriers and estimates symbols in accordance with a QR decomposition algorithm. A unitary matrix is derived such that a product of a spreading matrix including spreading elements as its elements and a channel matrix representing radio channel states is equal to a product of the unitary matrix and a triangular matrix. A reception vector, a unitary matrix and a triangular matrix are used to estimate symbol candidates transmitted from individual transmit antennas.