We are developing a fast Fourier transform (FFT) processor using high-speed and low-power single-flux-quantum (SFQ) circuits. Our main concern is the development of an SFQ butterfly processing circuit, which is the core processing circuit in the FFT processor. In our previous study, we have confirmed the complete operation of an integer-type butterfly processing circuit using the AIST 2.5 kA/cm² Nb standard process at the frequency of 25 GHz. In this study, we have designed an integer-type butterfly processing circuit using the AIST 10 kA/cm² Nb advanced process and confirmed its high-speed operation at the maximum frequency of 50 GHz.