This paper presents a 10-Gbit/s bidirectional wireless data transmission system using 120-GHz-band orthomode transducers (OMTs). The OMTs are used for polarization division duplex bi-directional transmission of 120-GHz-band wireless link. We designed and fabricated a new finline OMT which is adjusted for the spectrum of ASK modulation. The measured isolation is more than 59dB at a carrier frequency of 120-GHz-band wireless link. Using the finline OMT, we developed new 10-Gbit/s bidirectional wireless equipment. With this wireless equipment, we succeeded in experiments for 10-Gbit/s bi-directional wireless data transmission and for seamless connection to 10 Gigabit Ethernet (10GbE).