The oscillation voltage (Ebm) is an important parameter of the characteristic constants of a magnetron. When Ebm is made high, it serves so as to be able to improve the efficiency of a magnetron. Thus, the magnetron with 7% higher oscillation voltage than the former one is developed by Matsushita Electric Industrial Co.Ltd, In addition to this, the reduced harmonic type AC-DC converter suitable for driving this magnetron is proposed lately. This inverter type converter has the voltage-boost function of an active clamp scheme with soft switching pulse modulation strategy topology. This paper describes a novel type of active clamp AC-DC converter circuit and the operation of this converter which was developed. The operating characteristics of this soft switching converter are evaluated from a practical point of view as compared with the conventional converter.