PURPOSE: To enable a remote measurement of resistance and current in a wide range by a method wherein a voltage is applied between measuring terminals in a power supply system in a atomic reactor, etc. and the generated current is processed through an arithmetic operation.

CONSTITUTION: When measurement voltage 0W1,000V is applied to terminals 11 through a high voltage regulator 27, a leak current Iin in accordance with an insulation resistance of a measurement object flows between terminals 11. And then, a power source voltage is applied to a logarithm amplifier 30 which is connected through an ammeter 28 and a resistor 29 to the earthing side terminal of the terminal 11, via a low voltage regulator 24. And the leak current Iin from the terminal 11 is operated and amplified according to a logarithmic function and the operated signal is supplied to an isolation amplifier 31 connected to a low voltage regluator 25. The output voltage thereof is converted into a current through a converter 32 and an analog unified signal of 4W20mA is sent from a terminal 12 to a transmission line and a display system.