PURPOSE: To make it possible to elevate the measuring precision and shorten the measuring time, by utilizing a charged capacitor as the power source in case a variation of the electric characteristic to variation of the applied voltage is measured.

CONSTITUTION: When measuring the characteristic, at first the DC power source 7 is set to the maximum source voltage to be measured, and the electrolytic capacitor 8 for the power source is charged with electricity by turning ON the power source switch 10. As a result, the electronic circuit to be measured on the electronic parts, for instance, the operation amplifier 1 also becomes an active state at the same time. Subsequently, when the switch 10 is turned OFF, the capacitor 8 starts electric discharge in a state that the operation amplifier 1 and the resistor 9 for electic discharge are made load, and is varied to "0" V. Thus, since the source voltage of the operation amplifier 1 is free from a mechanical external noise such as a brush noise owing to the voltage in case the capacitor 8 discharges, the characteristic can be measured precisely.