A three-phase transformer according to an embodiment includes a first plate iron core and a second plate iron core disposed opposite each other; a plurality of columnar iron cores disposed between the first plate iron core and the second plate iron core so as to be connected to the first plate iron core or the second plate iron core, the number of the columnar iron cores being an integer multiple of 3, the columnar iron cores being disposed rotation-symmetrically with respect to an axis equidistant from central axes of the columnar iron cores; and coils including a plurality of primary coils and a plurality of secondary coils, the number of the primary coils being an integer multiple of 3, the number of the secondary coils being an integer multiple of 3, the primary coils and the secondary coils being wound on the individual columnar iron cores.