To simplify structure in a three-phase voltage-controlling transformer assembly for controlling an output voltage at a non-step mode.

The three-phase voltage-controlling transformer assembly includes three sets of first to third transformers each comprising first and second transformers. One set includes a first transformer with an input winding and an output winding around an iron core with a closed magnetic path, and a second transformer with an input winding and an output winding wound in a reverse polarity to the winding of the first transformer around the iron core in the closed magnetic path. The input winding of the first transformer in each set is connected in series to the input winding of the second transformer, three sets of input windings are constituted in delta connection topology, and each of the connecting points is connected to each of U, V, W phases in a three-phase AC supply through reactors L1, L2, L3. Further, the output winding of the first transformer in each set is connected in series to the output winding of the second transformer in star connection topology, and loads Z1, Z2, Z3 are connected in between the star-connected terminals. At the same time, a control winding C is wound around each of the iron cores in the closed magnetic path in three sets of transformers to control an output voltage by a DC current flowing through the control winding C.