PURPOSE: To measure the loss and resistance of a large current feeding conductor when a large current is fed by applying a voltage obtained by rectification and measuring a load current and a load voltage, and finding the load resistance and loss through arithmetic based upon the measurement results.

CONSTITUTION: The voltage of a commercial AC power source 1 is rectified by a rectifying circuit 2, and applied to a high frequency inverter 4 through a capacitor 3 and converted into a high frequency alternating current, which is rectified by a rectifying circuit 6 and applied to a load 9. The voltage drop across a serial resistance 8 interposed in a feeding path to the load 9 in series is amplified by a current amplifying circuit 10 to obtain a current signal I, and the voltage across the load 9 is amplified by an amplifying circuit 11 to obtain a voltage signal V; and both signals I and V are applied to an arithmetic circuit 11. Then, the circuit 11 perform the arithmetic to calculate the load resistance, loss, etc., so the load voltage V0 and load current I0 are measured while a large current is flowed to the load 9, and the resistance, loss, etc., in actual use are measured accurately. Further, the high frequency is rectified and applied to the load,so a high frequency transformer may be sized small and the whole instrument is reduced in size.