A single phase inverter for supplying power to a load comprising, a bridge circuit (Q u, Q v, Q x, Q y) including a series connection between a first main switching element and a second main switching element and a series connection between a third main switching element and a fourth main switching element, the series connections configured to be connected in parallel with respect to a DC power source, and each of the main switching elements being connected to a diode (D u, D v, D x, D y) in parallel, reverse-biased with respect to the DC power source, a smoothing circuit configured to be connected to the DC power source, an auxiliary switching circuit whose input terminals are connected to the output terminals of the smoothing circuit, a resonant capacitor (C 2, 4) whose terminals are connected to the output terminals of the auxiliary switching circuit, the bridge circuit being connected in parallel to the resonant capacitor (C 2, 4); and a resonant inductor (L, 6, 6A, 7) whose first terminal is connected to a connection point of the first main switching element and the second main switching element, in the bridge circuit, the second terminal of the resonant inductor being configured to be connected to the load, wherein the resonant capacitor (C 2, 4) and the resonant inductor (L, 6, 6A, 7) form a resonance circuit, when an open operation by the auxiliary switching circuit disconnects the smoothing circuit from the resonant capacitor (C 2, 4), and a) in a switching operation by a main switching element of said main switching elements from an off-state to an on-state, a resonance current of the resonance circuit passes through the diode (D u, D v, D x, D y) being connected in parallel with the main switching element (Q u, Q v, Q x, Q y), thereby achieving zero current switching for the main switching element, and passing of the resonance current through the resonance circuit makes voltage across the main switching element to be zero voltage, thereby achieving the zero current switching and zero voltage switching for the switching operation by the switching element from the off-state to the on-state; and b) in the switching operation by a main switching element of said main switching elements from the on-state to the off-state, discharging of the resonant capacitor (C 2) with the resonance current makes the voltage across the capacitor to be zero voltage, and the voltage across the main switching element becomes zero voltage, thereby achieving the zero voltage switching for the switching operation by one of the main switching elements from the on-state to the off-state, and the switching operation by the main switching elements is performed by soft switching. a) in a switching operation by a main switching element of said main switching elements from an off-state to an on-state, a resonance current of the resonance circuit passes through the diode (D u, D v, D x, D y) being connected in parallel with the main switching element (Q u, Q v, Q x, Q y), thereby achieving zero current switching for the main switching element, and passing of the resonance current through the resonance circuit makes voltage across the main switching element to be zero voltage, thereby achieving the zero current switching and zero voltage switching for the switching operation by the switching element from the off-state to the on-state; and b) in the switching operation by a main switching element of said main switching elements from the on-state to the off-state, discharging of the resonant capacitor (C 2) with the resonance current makes the voltage across the capacitor to be zero voltage, and the voltage across the main switching element becomes zero voltage, thereby achieving the zero voltage switching for the switching operation by one of the main switching elements from the on-state to the off-state, and the switching operation by the main switching elements is performed by soft switching.