Abstract: A microwave transmitting and receiving apparatus comprises a Gunn diode as an oscillating element and a mixer diode as a receiving element disposed within a rectangular waveguide closed at one end by its short-circuiting plate. The oscillating and receiving elements are juxtaposed with each other at a position spaced by 1/2 .lambda.g (.lambda.g: wavelength in the waveguide) from the short-circuiting plate toward an opening of the waveguide. An adjusting screw for permitting a match of the receiving element impedance with the input signal impedance and for adjusting the output power is fitted by screw engagement to the waveguide at a position spaced by 1/4 .lambda.g from a straight line connecting the both elements toward the waveguide opening, and another adjusting screw for oscillating frequency-adjustment is fitted by screw engagement to the waveguide at a position between said straight line and the short-circuiting plate.