1. A measuring apparatus for measuring a value of at least one passive element value using a current vector, comprising: a sine wave oscillator for supplying a sine wave having a constant voltage amplitude and frequency to the passive element; a voltage detecting unit for detecting a voltage drop across the passive element where the sine wave is applied, said voltage detecting unit comprising a differential amplifier for comparing voltage drops at either end of the passive element to be measured, so that a difference thereof can be amplified; a current detecting unit for detecting a current vector flowing through the passive element when the sine wave is applied, said current detecting unit comprising an operational amplifier for receiving current flowing through the passive element at an inverting terminal and a resistor for feedback of a current signal output from the operational amplifier; a phase shifter for shifting a voltage drop output from the voltage detecting unit; a multiplying circuit unit for multiplying an output of the current detecting unit by an output of the phase shifter to calculate a phase difference between the voltage and current; a first mean value calculating unit for calculating a mean value of the phase shifted voltage drop output from the phase shifter; a second mean value calculating unit for calculating a mean value of the output from the current detecting unit; a filter unit for filtering an output of the multiplying circuit unit to obtain a direct current component from the output of the multiplying circuit unit; an analog-to-digital converter for converting the respective outputs of the first and second mean value calculating units and the output of the filter to digital signals; a microcomputer for performing an operational process on the digital signals output from the analog-to-digital converter; and a display unit for displaying a result operationally processed at the microcomputer.