PURPOSE: To achieve a high resolution without using a high-frequency clock and to obtain measurement data inexpensively and in real time in a distance measuring instrument for obtaining the distance to an object to be measured according to the turn around time of electromagnetic wave.

CONSTITUTION: The electromagnetic wave pulse of a transmitter 2 which is transmitted to an object to be measured and the reflection wave pulse received by a receiver 3 are synthesized by a pulse synthesizing circuit 4, a pulse signal corresponding to the time difference between transmission and reception is generated, and a capacitor is charged by the amount of the pulse signal by a constantcurrent charging circuit 8. Then. the peak voltage of the capacitor is held for a constant amount of time by a peak hold circuit 9 and then the distance from the peak voltage to the object to be measured is calculated.