U-tokyo group has been developing heterodyne receivers for Terahertz astronomy. Recently, we have successfully developed the 3.1 THz heterodyne receiver by using a Terahertz Quantum Cascade Laser fabricated at National Institute of Information and Communications Technology (NICT) as a local oscillator and a quasi-optical Hot-electron Bolometer (HEB) mixer fabricated in our laboratory. This is the first heterodyne detection of a HEB mixer using the NbTiN film as a superconducting material in this frequency region. The DSB receiver noise temperature is evaluated to be 5600 K. When the optical loss is corrected, it is as low as 2100 K. This value is almost the same level of the NbN HEB mixer in this frequency region. This is a collaborative study with Dr. Hiroyuki Maezawa of the STE Laboratory in Nagoya University and Drs. Yoshihisa Irimajiri, Norihiko Sekine, and Iwao Hosako of NICT.