In this paper, a surfer wide-band FM lossy-line discriminator is investigated, as it has the merit of rediucing the dimensions of the discriminator by using proper dielectric material in the transmission tine. It is shown that the lossy-line discriminator that is made of a pair of the transmission lines satisfying the distortionless condition approximately gives almost no more deterioration in its characteristics than the ideal-line FM discriminator, while the dimensions of the transmission lines of the discriminator can be reduced greatly.