A receiver for use in a mobile communication system using a MC-CDMA scheme and a MIMO transmission scheme, wherein in the mobile communication system, a set of symbols in a sequence of transmission symbols together with spreading codes for code multiplexing is converted into a code-multiplexed signal, and inverse Fourier transform is performed on the converted code-multiplexed signal, and the resulting signal is transmitted from multiple transmit antennas, the receiver comprising: an extraction unit configured to perform Fourier transform on signals received at multiple receive antennas and extract signal components of individual subcarriers; and a signal detection unit configured to apply a QR decomposition algorithm to the extracted signal components and estimate a transmission symbol, wherein the signal detection unit includes: a decomposition unit configured to find a unitary matrix such that a product of a spreading matrix and a channel matrix is equal to a product of the unitary matrix and a triangular matrix, the spreading matrix having the spreading codes for the code multiplexing as matrix elements, and the channel matrix representing radio channel states between the transmit antennas and the receive antennas; and an estimation unit configured to use the triangular matrix and a vector to estimate transmission symbols transmitted from the individual transmit antennas, the vector resulting from multiplication of the unitary matrix with a reception vector including the signal components received at the receive antenna. an extraction unit configured to perform Fourier transform on signals received at multiple receive antennas and extract signal components of individual subcarriers; and a signal detection unit configured to apply a QR decomposition algorithm to the extracted signal components and estimate a transmission symbol, wherein the signal detection unit includes: a decomposition unit configured to find a unitary matrix such that a product of a spreading matrix and a channel matrix is equal to a product of the unitary matrix and a triangular matrix, the spreading matrix having the spreading codes for the code multiplexing as matrix elements, and the channel matrix representing radio channel states between the transmit antennas and the receive antennas; and an estimation unit configured to use the triangular matrix and a vector to estimate transmission symbols transmitted from the individual transmit antennas, the vector resulting from multiplication of the unitary matrix with a reception vector including the signal components received at the receive antenna. a decomposition unit configured to find a unitary matrix such that a product of a spreading matrix and a channel matrix is equal to a product of the unitary matrix and a triangular matrix, the spreading matrix having the spreading codes for the code multiplexing as matrix elements, and the channel matrix representing radio channel states between the transmit antennas and the receive antennas; and an estimation unit configured to use the triangular matrix and a vector to estimate transmission symbols transmitted from the individual transmit antennas, the vector resulting from multiplication of the unitary matrix with a reception vector including the signal components received at the receive antenna.