PURPOSE: To shorten a measurement time by directly converting the Q value and series resistance value of a diode into resonance high-frequency voltage values by using a parallel resonance circuit, and then by measuring the Q value and resistance value by converting them into DC voltage values.

CONSTITUTION: The measurement circuit is provided with oscillator 13 oscillating at a special measurement frequency and voltage, coupling capacitor 20, local oscillator 22, mixer 23, and intermediate-frequency amplifier 24. In addition, this is equipped with detector 25, circuit 26 operating as both a DC amplifier and highest- voltage holding circuit, DC voltmeter 27 for directly reading a Q value or series resistance and comparator circuit 28. In this constitution, high-frequency voltage e1 of oscillator 13 determined by Q or series resistance Rs of the diode is applied to mixer 23 and then transmitted in a form of an intermediate-frequency signal to amplifier 24. Next, this is detected and converted into a DC signal by detector 25, amplification-held by circuit 26, and read by voltmeter 27 simultaneously with the comparison by circuit 28, so that the Q value and resistance value Rs will be selectively discriminated.