PURPOSE: To increase the number of stable operation point without increasing the number of stage of a negative resistance characteristic in a multi-differential negative resistance element in a multistage variable conductance circuit.

CONSTITUTION: The multi-differential negative resistance element 1 having two stages of negative resistance characteristics and a normally-on type load FET 5 are connected in series, and the gate electrode of the FET 3 as a variable conductance element is connected to the connection point. Further, the multi-differential negative resistance element 2 having two stages of negative resistance characteristics and the normally-on type load FET 6 are connected in series, and the gate electrode of the FET 4 as the variable conductance element is connected to the connection point. Then, both FETs 3, 4 are connected in series. In such a manner, by using two sets of multistage variable conductance circuits, the number of operation point of the variable conductance is increased, and then the number of stable operation point is increased.