Abstract: A method of adjusting a phase shift in an amplification multicavity klystron comprises the steps of tapping a portion of signal from output and intermediate resonators of a klystron, adding up the tapped signals, adjusting the amplitudes and phases of the tapped signals so that said signals have equal amplitude but opposite phases with the klystron operating under nominal conditions and applying the sum signal to an input resonator whereupon anode voltage is varied until a phase shift in the klystron changes, the subsequent step being the selection of the phase of the sum signal to provide for a minimum phase-shift variation in the klystron. A device for executing the proposed method of adjusting a phase shift includes a line composed of a phase shifter, an adder, and an additional phase shifter. One input of the phase shifter is connected to the output resonator of the klystron, while the other input thereof is coupled to the adder.