To receive a stable image signal, etc., without being affected by an external noise by separating an inputted polarization plane modulation signal into a P-polarized light signal component and an S-polarized light signal component, converting them into electrical signal, and also, extracting a specific frequency component, and compositing them, thereafter, demodulating the variation of the polarization plane as an analog intensity signal.

The polarization plane modulated light is converted to collimated beams of light through a collimating lens 2, then, the light is separated into the P- polarized light signal component and the S-polarized light signal component through a polarizing prism 3, thereafter, both components are separately converted into the electric signals by optic/electric converters 4 and 7. As for the outputs of the converters 4 and 7, the frequency component only in the required band is extracted by a band filter with the same frequency characteristics so as to be converted into an electric vector signal composited with an electric signal vector by an electric vector synthesis circuit 6. The electric vector signal is demodulated by a phase detection circuit 10 as the analog intensity modulation signal being proportional to the rotational angle of the polarization plane, then, a demodulation signal 12 is obtained.