PURPOSE: To reduce the size of the device and enable fast real-time processing and high-frequency signal processing by inputting a light signal modulated with an analog electric signal to a prism and then performing Fourier transformation.

CONSTITUTION: This device consists of an electrooptical conversion part 10, the prism 20, and an optoelectrical conversion part 30. The optoelectrical conversion part 30 inputs the analog electric signal S1 and outputs a modulated laser beam signal S having its amplitude modulated with the analog electric signal S1. The prism 20 inputs the modulated laser beam signal S2 and outputs optical signals S21, S22... having their sideband waves processed by Fourier transformation. The optoelectrical conversion part 30 inputs the optical signals S21, S22... after the Fourier transformation, converts them into electric signals in order, and outputs the analog electric Fourier-transformed signal S3.