To expand the interval of repeaters on a hybrid optical transmission line.

A hybrid transmission line block 200 is constituted by connecting an EE fiber 10-1 having a large effective cross-sectional area, a fiber 11 having a small effective cross-sectional area, and an EE fiber 10-2 having a large effective cross-sectional area. Excited light from an optical repeater 150 is supplied from the side of the EE fiber 10-2 having the large effective cross-sectional area. Thus, the power of the excited light can be set sufficiently high and Raman amplification can be generated in the EE fiber 10-2 and the fiber 11. In such a case, by locating the fiber 11 almost in the center of the hybrid transmission line block 200, an optical SNR (signal-to-noise ratio) can be most improved, so that the interval of repeaters can be expanded.