To compensate a waveform distortion by using a nature that a spectral shape is perfectly retained even if all the linear distortions occur on a time-axis. An optical pulse transmitted from an optical pulse transmitter (1) via an optical fiber transmission line (2) is transmitted. An optical Fourier transformer (3) receives an optical pulse, and optically Fourier-transforms an optical pulse on a time-axis onto a frequency-axis to reproduce the frequency spectrum of an optical pulse on a time-axis be effecting switching between frequency and time, thereby compensating a waveform distortion by a linear effect on the optical fiber transmission line (2). A photodetector (4) receives an optical pulse from the optical Fourier transformer (3) and transforms this into an electrical signal to thereby obtain a pulse waveform before a transmission over the optical fiber transmission line (2).