Abstract: The present invention is disclosed to provide an inverter allowing a remarkable reduction in the number of parts used for an inverter unit which can improves the efficiency and allows current control in a wide range.Namely, the inverter unit for converting a direct current supplied from DC power supply, into an alternating current by conversion means alternatively converting the flowing direction of direct current by SWITCH ON/SWITCH OFF operation of a switching element, comprises a series resonance circuit formed at the primary side of a step-up transformer, a control means for switching ON/OFF said series resonance circuit by the switching element at a timing led in phase from the resonant frequency of this resonance circuit, and a load connected at the secondary side of the transformer, so as to solve the problems described above.