PURPOSE: To inexpensively manufacture the microwave oscillator and to reduce a temperature change in the oscillating frequency by making a casing of a plastic.

CONSTITUTION: An oscillation circuit is formed on the surface of a dielectric board 21 and a ring pattern 29 is formed around the circuit. A plastic-made cover 31 on the surface of which a metallic layer 32 is plated is adhered opposite to the ring pattern 99 to enclose the oscillation circuit. Lead wires are led to a rear side through the dielectric board 21, and an earth lead 30 being one of them and the metallic layer 32 are connected to shield the oscillator. A tuning screw 35 is provided to a ceiling of the cover 31 and a gold plating layer 34 to be connected to ground is formed to the rear side of the dielectric board 21.