To facilitate load torque measurement and miniaturize the measuring apparatus by measuring an input of a driving motor using a transducer and by detecting the load torque of a mechanism part of an on-load tap changer.

A current and a voltage of a driving motor 4 are received from a motor operating mechanism 1 by a transducer 8, and a primary side input of the driving motor 4 is measured. Then, in order to convert this primary side input into a load torque, a transducer input conversion value W and a transducer output voltage E are converted into an input of a motor by P1=W(E-1), and this input P1 is converted into a motor output torque T by T=(P1×η1÷(9.8×2π×Nr/60), where η1 denotes efficiency between the motor and the secondary and Nr denotes number of revolution of the motor, and the torque T is converted into load torque T0 by T0=T×i×η2, where i denotes a reduction ratio of the motor operating mechanism and η2 denotes efficiency, and thus obtained load torque T0 is recorded in a recording and measuring part in this load torque measuring apparatus for an on-load tap changer.