To provide a wavelength multiplex optical communication system that is accessed simply at a low cost in an optical communication network having branched optical fiber lines.

The wavelength multiplex optical communication system is provided with a 1st system where a signal light at a 1st wavelength band sent from a 1st optical transmitter 1-1 to optical subscribers 6-1-6-8 via a passive optical communication network and with a 2nd system where a signal light at a 2nd wavelength band sent from a 2nd optical transmitter 1-2 to the optical subscribers 6-1-6-8 via a passive optical communication network. The passive optical communication network is provided with an optical transmission line 2, a branching device 3, a 2nd optical filter 4 and an optical fiber line 5, the 1st optical transmitter 1-1 is provided with a light source 7, a 1st optical filter 8 and a multiplier 9, and each light guide path being a component of the 1st optical filter 8 and the 2nd optical filter 4 has a wavelength band pass filter element that passes one wavelength but stops other wavelength in the 1st wavelength band.