To provide a simplified structure of stopper mechanism for preventing a driving axis from rotating during completing energy storing of an energizing spring of a change-over switch used in a vacuum valve type on-load tap changer.

A stopper mechanism 30 for preventing a driving axis 4 from rotating during energy storing of an energizing spring 6, consists of a sub-cum 31 fixed to a driving cum 16 which has a stopper on the cum surface for driving a vacuum valve Mbw; a sub-cum follower 32 abutting to the cum surface of the sub-cum 31; and a sub-cum follower energizing spring 33 for energizing the sub-cum follower to the cum surface side of the sub-cum, and prevents the driving axis 4 from rotating during completing the energy storing of an energizing spring 6 by engaging the stopper on the cum surface of the sub-cum 31 with the sub-cum follower 32.