Abstract: Disclosed is an apparatus for measuring an optical transmission line property, which has: a pair of up and down optical fiber transmission apparatuses, each of which includes an optical transmission end office which includes a plurality of signal light sources for outputting signal lights with different wavelengths and an optical multiplexer for multiplexing the signal lights, an optical fiber transmission line and an optical reception end office which includes an optical divider for dividing the signal lights multiplexed and an optical receiver corresponding to each of the signal lights divided with different wavelengths; an optical turn circuit which includes an optical multiplexer and an optical divider and leads a part of light transmitting through the optical fiber transmission line to another optical fiber transmission line; andan optical power measuring circuit for measuring optical power distributions of a signal light propagating on the optical fiber transmission line and another signal light led to