PURPOSE: To make it possible to measure the electric characteristics of a piezoelectric oscillator with high accuracy at a high speed, by detecting the resonant impedance of the piezoelectric oscillator based on a voltage across both ends of a reference resistor, the output power of an amplifier and the resistance value of the reference resistor.

CONSTITUTION: A piezoelectric oscillator 2, which measures electric characteristics, is connected between measuring terminals 16 and 17, which are provided between the output of an amplifier 11 and the input of a phase correcting amplifier 12. A variable resistor VR is connected between the output of the phase correcting amplifier 12 and the ground. The resistor VR sets a measuring voltage, which is applied to the piezoelectric oscillator 2. A resistor R of a time constant circuit 13 is connected between the slider of the resistor and the amplifier 11. A capacitor C of the time constant circuit 13 is connected between the input of the amplifier 11 and the ground. The resistor R of the time constant circuit is a variable resistor. The resonant frequency and the resonant impedance of the piezoelectric oscillator 2 can be measured.