Distance measuring system

A distance measuring system, comprising a laser light source for projecting a pulsed laser beam to an object to be measured, a photodetection element for receiving an external light reflected by the object to be measured and an internal light which is a divided part of said laser beam, a photodetection element including said photodetection element, and a control arithmetic unit for calculating a distance based on photodetection of the external light and the internal light received by said photodetection element, wherein said photodetection circuit forms non-detecting condition, and the non-detecting condition is formed before or after photodetection timing of the internal light.