PURPOSE: To display a frequency deviation, etc., automatically on the same range full scale irrelevantly to a signal to be measured by correcting the pulse width of a signal based upon the phase difference between two signals with the frequency of the signal to be measured.

CONSTITUTION: Schmitt trigger circuits 1a and 1b shape the waveforms of the signal to be measured and send their outputs to a phase comparator 2. The phase comparator 2 detects the frequency or phase difference of the signal to be measured and sends it output to a quantizer 4. The quantizer 4 samples the input signal according to a clock signal to quantize it with a digital signal. A signal processing circuit 5 stores the digital signal for a specific time and divides its data by constant phase time. A digital-analog converter 6 converts the digital signal into an analog signal, which is inputted to an analog display device.