A noise shielding apparatus for the magnetron of a microwave oven for preventing the lowering of the voltage resistance of the capacitor due to the poor concentricity and the poor interfacial state is disclosed. A shielding case has a side wall with an elliptic opening and a projected portion along the elliptic opening by bending out a circumference portion thereof. The capacitor includes an elliptic cylindrical ceramic dielectric, separate electrodes separately formed on an upper surface of the ceramic dielectric and a common electrode formed on a lower surface of the ceramic dielectric. Through conductors pass through the through holes and are connected to a choke coil of the magnetron. Each of through conductors is provided with an electrode connection portion for electrically connecting with the separate electrodes integrally and horizontally formed from around an upper portion of each of through conductors. An insulation lattice is formed at a central upper portion of the insulation case over a border line of the separate electrodes. Forming the electrode connection portion prevents the poor perpendicularity and/or poor interfacial state. Providing the insulation lattice solves simply and stably the insulation problem between fastening tabs and thus the magnetron may be stably operated.