PURPOSE: To get a frequency area reflectometry measuring instrument which can automatically measure the accurate position of the break point or the discontinuous point of a cable.

CONSTITUTION: This measuring instrument is equipped with a sweep part oscillator 16, which generates sweep part frequency changing at known rate of change, the first frequency converters 14, 18, and 24, which generates middle frequency FI from the signal of a signal i/o terminal, the sweep part frequency, and reference frequency, and an offset oscillator 26, which generates variable offset frequency. Furthermore, it is equipped with the second frequency converter 28, which generates wireless frequency from the variable offset frequency and sweep part frequency and supplies this wireless frequency to a signal i/o terminal, a frequency measuring means 44, which measures the frequency, severally, and a control means 32, which adjusts the offset quantity of an offset oscillator while monitoring the amplitude of middle frequency and calculates the position of the discontinuous point of a cable to be measured.