PURPOSE: To prevent the thermal destruction of the semiconductor to be measured by limiting the current flowing to the semiconductor, and thus to secure the automatic measurement for the dielectric strength of the semiconductor.

CONSTITUTION: High voltage rectangular wave generator circuit 32 generates the rectangular wave going up linearly via the control input signal. And the active resistance of measured semiconductor 33 reduces at t1 and with the time point of voltage 6 of the rectangular wave, thus current I1 flowing. Current I1 is detected via current detector circuit 34 to produce the feedback signal, and the generation voltage of circuit 32 is kept constant (holding time t2) by the feedback signal. Then the feedback signal is used as the measurement control signal, and the value of voltage v1 is measured through voltage measurement circuit 35 to be displayed via display circuit 36 as well as to be transmitted outside in the form of the data output. Here, point b shows the time point when the impedance of semiconductor 33 begings to lower, and thus the breakdown voltage of 33 is measured through point b. System control circuit 31 transmits the measurement end signal outside as the control output when t1 and t2 are through.