In a gyrotron comprising a cathode with an emitter ring, an accelerating anode, a resonator, a collector, and an uncoupling conduit, an arrangement is disposed around the resonator which generates a solenoidal static axial magnetic constant field which, in the area of the resonator, assumes a predetermined wave form causing the electrons emitted from the cathode to move along a spiral path and which has varying localized strengths such that the electrons passing therethrough along the spiral path have, upon exiting the resonator area, only an insignificant transverse velocity component left, whereupon they are attracted by the collector which is precharged.