To easily realize a stable operating characteristic and high current amplification factor by automatically adjusting an operating point of an FFT (flux flow transistor), i.e., a bias condition and to provide a good flux flow transistor circuit by adapting the operating characteristic and the current amplification factor to an analog circuit or a digital circuit.

The flux flow transistor circuit is constituted by providing an input terminal (input signal line) 11 on which an input signal Ictrl is applied, the FFT 10 to perform a specified amplification processing, an output terminal (output signal line) 12 from which an output signal lout amplified by the FFT 10 is outputted and a feedback circuit (feedback means) 20 to feed the output signal Iout back to the input side of the FFT 10.