PURPOSE: To facilitate the separation of a demodulated component and to obtain a large output by generating a pulse with specific width every time when a pulse changes in state and increasing the frequencies of higher harmonic components double.

CONSTITUTION: A signal (a) inputted to an input terminal 101 and then converted into a binary signal is delayed as shown by (b) through the delay circuit consisting of exclusive OR circuits 102 and 104 and then ORed exclusively with the original signal (a) to output pulses with pulse width Td as shown by (c) in every change in state. A monostable multivibrator 106 extends the pulse width Td to Tm and a smoothing circuit 107 extracts a low frequency component (demodulated component) (d). Then, two kinds of state changes are detected by kinds and those pulses are increased in pulse width respectively and then added together to obtain a large demodulation output.