The switching timing is flexibly set in an inverter.An H-bridge circuit is controlled based on a triangular wave signal and an error voltage. To control the circuit, a first high-side transistor and a second low-side transistor are turned on in a first period until the triangular wave signal reaches the error voltage. The first high-side transistor is turned on in a second period until the triangular wave signal reaches a peak edge. A second high-side transistor is turned on in a third period until the triangular wave signal reaches a bottom edge. A first low-side transistor and the second high-side transistor are turned on in a fourth period until the triangular wave signal reaches again the error voltage. The second high-side transistor is turned on in a fifth period until the triangular wave signal reaches again a peak edge. The first high-side transistor is turned on in a sixth period until the triangular wave signal reaches again a bottom edge.