PURPOSE: To effectively attenuate an unrequired frequency noise from a high frequency oscillator and prevent its leakage into the outside of a main body by shielding a lead wire that is connected to a heater input terminal with a metal net or the like and connecting this sealing section and a metal case electrically.

CONSTITUTION: The frequency noise leaked outside a high frequency oscillator 4 without being attenuated by in the filter of the high frequency oscillator 4 cannot be leaked into a main body 1 from a heater input terminal section 9 since it is covered with a metal case 10. Therefore, it is directed to the side of a transformer 5 through a lead wire 6, but since the lead wire 6 is shielded 7 with a metal net or the like and the shielding section 7 is grounded in a chassis, the whole lead wire 6 changes into a type of a penetration type capacitor. As a result, the frequency noise is remarkably attenuated through the lead wire 6 by the electrostatic capacity between this lead wire 6 and the shielding section 7.