An on-load tap changer which ensures the compatibility of an oil tank when an interchange from the in-oil arc switching scheme to the vacuum-valve scheme is made, improves a retrofit function, achieves a space saving by simplifying components, and facilitates a construction of an actuation mechanism is provided. A change-over switch 46 for the vacuum-valve scheme is placed in an oil tank 50 filled with an insulation oil 56. The change-over switch 46 is provided with a main contact contained in vacuum valves 2, 3, 5, 6, and current-carrying conductors 7, 8 to reduce a current flowing in the main contact, and parallel link mechanisms actuating the current-carrying conductors 7, 8 in a parallel manner. A stationary contact 47 capable of contacting with and separating from the current-carrying conductors 7, 8 is attached to the internal wall surface of the oil tank 50. The change-over switch 46 is freely attachable to and detachable from the oil tank 50 with the stationary contact 47 being attached to the oil tank 50.