PURPOSE: To improve the frequency stability of an oscillating multiplier and, at the same time, to increase its output under a low-noise condition, by setting the length of the open strip line for short-circuiting of a dummy load to λg/4(2n-1) (where, λg is the wave length of fundamental wave and (n) is an integer).

CONSTITUTION: A cavity 11, cut-off waveguide 12, and output waveguide 13 are formed in a metallic box body 10 and a basic oscillating section composed of a semiconductor element 14 for oscillation, microstrip lines 16 and 18 formed on a ceramic 15, dummy load 17, and dielectric resonator 19 installed through a spacer 20 is contained in the cavity 11. Moreover, another dielectric resonator 22 is installed to the frequency adjusting screw 24 of the waveguide 12 through a spacer 23 and the frequency adjusting screw 26 of the resonator 19 is installed to a metallic cover 25. Then the length l2 of a line 18 is set to λg/4(2n-1) and the element 14 and line 16 are connected with each other with a gold ribbon.