PURPOSE: To easily perform high-grade arithmetic processings by separating modulated carrier waves to negative and positive frequency components and demodulating them by a specific circuit.

CONSTITUTION: By a conversion means formed of a local oscillator 1, multipliers 2 and 3 and LPFs 4 and 5, modulated carrier wave signals are moved to a band over the frequency 0. Then, by a separation means formed of a π/2 shifter 6 using a weber circuit and adders 7 and 8, the negative frequency component and the positive frequency component are separated. By using both frequency components and performing demodulation, a frequency band to be processed can be narrowed to a half, the throughput of a digital signal processor is improved and a cost can be reduced.