PURPOSE: To realize the arbitrary negative resistance of a prescribed value extending over a wide high frequency band.

CONSTITUTION: A phase adjusting part 12 and a gain adjusting part 13 are cascaded to a transistor amplifying circuit 11 in which input and output terminals are matched and have high isolation, and the phase and the gain are set so that the composite impedance between an input and an output becomes Z1=-(S21-1)ZO against the target characteristic impedance ZO. Thus, the impedance Z1 of a desired value including a negative resistance by a high frequency is synthesized, and also, by compensating a fact that the phase of a forward direction scattering coefficient S21 of an S parameter of an amplifier is varied by a frequency by adding the parallel impedance element Z1 the negative resistance of a prescribed value is realized extending over a wide band.