A microwave magnetron-type device comprises at least one anode block with annular metal straps electrically associated with respective vanes of the anode block cavities, having the same polarity at -mode. The straps of different polarities, electrically associating respective vanes of the same polarity, are paired, each pair being arranged with respect to one another along the anode block axis to form a single multistage retardation system. The device also comprises a means for creating a magnetic field directed along the anode block axis enveloping said anode block, and a means for increasing the magnetic field density in direct proximity to the anode block end faces, forming a gap with the end faces of the anode block. At least some of said straps are made at least partically of a magnetic material, and the mass of this material is so distributed along the anode block axis that the magnetic field density varies along the anode block axis as follows: ##EQU1## where B.sub.x is the variation in the magnetic field density along the anode block axis;B.sub.O is a constant component of the homogeneous magnetic field density along the anode block axis;B.sub.O1 is the amplitude of variation in the magnetic field density along the anode block axis, over its length X.sub.1, which does not exceed 50% of B.sub.O ;B.sub.O2 is the amplitude of fluctuation of the magnetic field density from one pair of retardation system straps to another along the anode block axis, over its length X.sub.1, which does not exceed 20% of B.sub.O ;h is the spacing between strap pairs;n=1,2,3 . . . is a coefficient equal to the number of half-cycles of the cosinusoidal distribution of the amplitude of the high-frequency electric field of a respective mode.