In each anode vane 10, there is provided the brazing material spreading prevention groove 13 that interconnects the strap ring inserting portions 11 and 12 in parallel to the direction of the central axis Ax. With such a configuration, it is possible to prevent the residual brazing material 3a from spreading to the front end part 10a of the anode vane 10 when each anode vane 10 is brazed on the inner peripheral surface of the anode cylinder 1. Therefore, non-uniformity in thickness of the anode vanes 10 caused by the residual brazing material 3a is suppressed, and electrostatic capacity between the anode vanes 10 adjacent to each other becomes substantially constant. Thus, it is possible to obtain stable resonant frequency. In addition, it becomes easy to perform adjustment for obtaining the stable resonant frequency in that non-uniformity in initial frequency of the time when the magnetron is completely assembled decreases.