PURPOSE: To change over output voltage by one three-phase no-voltage tap changer by providing a three-phase no-voltage tap changer, which changes over taps to a plurality of each lead-out terminal of firstWthird windings and is connected to them and star-connects the firstWthird windings.

CONSTITUTION: A three-phase transformer is constituted by a first fixed contact group 15aW15c connected to lead-out terminals 11aW11c, a second fixed contact group 16aW16c connected to lead-out terminals 12aW12c, a third fixed contact group 17aW17c connected to lead-out terminals 13aW13c and a travelling contact 18, which is constituted in a star shape and changes over and connects each fixed contact of the first, second and third fixed contact groups 15aW15c, 16aW 16c, 17aW17c. Output voltage is changed over by changing over the travelling contact 18 constituted in the star shape to the fixed contacts 15a, 16a, 17a or the fixed contacts 15b, 16b, 17b or the fixed contacts 15c, 16c, 17c.