PURPOSE: To demodulate a spread spectrum signal with a simple circuit by eliminating a harmonic component in the output of a multiplier circuit multiplying a reception signal with the output of a delay circuit.
CONSTITUTION: This demodulation circuit for a spread spectrum signal consists of a delay circuit 52 retarding a reception signal R(t) by the period T of a PN(Pseudo Noise) code, a multiplier 50 multiplying the output R(t-T) of the delay circuit 52 with the reception signal R(t) and a low pass filter 54. For example, a delay circuit having one period T of a PN code is formed by an analog delay line 52A and a digital circuit. That is, the reception signal passes through a low pass filter 52a, A/D-converted by an A/D converter 52b and the result is inputted to a shift register 52c. The output of the shift register is converted into an analog signal by a D/A converter 52d and the signal is outputted through a low pass filter 52e. Thus, a PN code synchronizing circuit and a carrier recovery circuit are not required and the spread spectrum signal is demodulated with simple constitution.