PURPOSE: To widen the contact area and to improve the cooling effect by forming a radiator such that the portion contacting with the outer-circumference of anode is linear.

CONSTITUTION: A cathode stem 2 and an output antenna terminal 3 are projected respectively on each side of anode 1 for magnetron, where the cathode stem 2 coindcides with anode axis Y while the X axis of the antenna terminal 3 does not coincide with anode axis Y but deviated by distance l. A radiator 4 is secured to the outer circumference of anode 1 and constructed by bending a rectangular aluminum plate or copper plate in meandering then forming a plurality of radiating fins 5 into a circle. The bending width of each fin 5 is not the same and the bending width L1 the at the position of anode axis Y against the antenna axis X is smaller than the width L2 at the opposite side. Consequently the contact area against the anode cylinder is wider resulting in considerable improvement of cooling effect.