PURPOSE: To attain the composition of large electric powers regardless of the use of small sized cores by connecting in parallel secondary windings of transformer systems each comprising plural unit transformers where the output of a high frequency electric power amplifier is applied to each primary winding and their secondary windings are connected in series.

CONSTITUTION: A high frequency signal outputted from power amplifier circuits 111-11n of a 1st group 11 is fed to primary windings of unit transformers T11-T1n. Furthermore, the high frequency signal outputted from power amplifier circuits 121-12n of a 2nd group 12 is fed to primary windings of unit transformers T21-T2n. Moreover, a 1st transformer system T1 is made up of the transformers T11-T1n and secondary windings of the transformers T11-T1n are connected in series. A 2nd transformer system T2 is made up of the transformers T21-T2n and secondary windings of the transformers T21-T2n are connected in series. Secondary windings of the 1st transformer system T1 and the 2nd transformer system T2 are connected in parallel.