The demand for radio-frequency (RF) power meter calibration in the mm-wave region has been growing, and the upper limit of the frequency for the calibration has reached the sub-terahertz region. For this reason the need for a reliable and practical primary standard for high frequencies is increasing. In this paper we report a new broadband rectangular waveguide (RW) calorimeter with a thermal feedback system (TFS) for the frequency range from 50 GHz to 110 GHz.