We developed a waveguide-type dual-polarization sideband-separating SIS receiver system of the 100-GHz band for the 45-m radio telescope at the Nobeyama Radio Observatory, Japan. This receiver is composed of an orthomode transducer and two sideband-separating SIS mixers, which are both based on the waveguide technique. The receiver has four intermediate frequency (IF) bands of 4.0--8.0 GHz. Over the radio frequency range of 80--120 GHz, the singlesideband receiver noise temperatures are 50--100 K and the image rejection ratios are greater than 10 dB. The new receiver system was installed in the telescope, and we successfully observed the 12CO, 13CO, C18O and the other emission lines simultaneously toward the Sagittarius B2 region to confirm the performance of the receiver system.