PURPOSE: To simultaneously complete the changing of a contact in an on-load tap changer and to reduce the weight and size of the changer by so constructing a movable sector plate instantaneously at predetermined angle.

CONSTITUTION: Respective phase stationary contacts A are arranged on the inner periphery of an insulating cylinder 21, and a movable sector plate 22 is pivotally secured rotatably through a pivotal shaft 25 formed on a connecting plate 24. When a drive shaft 23 is rotated due to the movement of the rack 36, the plate 22 is instantaneously rotated at predetermined angle by the operations of an energy storage lever 25 and an energy storage spring 30 to change the movable contact B. Further, a coupling 39 is provided to be detachable. Thus, it can simplify the quick-changing mechanism and reduce the size and weight of the changer.