To suppress uneven abrasions of the contacts of a changeover switch, by making alterable the resistance values of the current limiter resistors of an on-load tap change-over switch.

A current transformer is 2 provided to sense the load current of a transformer when loading it, and the resistance values of current limiter resistors Ra, Rb for suppressing inter-tap short-circuit currents in the tap changing-over processes of a changeover switch DS are made variable by the measurement values of the current transformer 2 and a decision circuit 3 to uniformalize the abrasion quantities of main contacts Ha, Hb and resistance contacts Wa, Wb of the changeover switch DS.