PURPOSE: To measure a distance to an object to be measured with high accuracy by providing an optical pulse generator for generating an optical pulse and a detector for detecting a reflected light generated by the object to be measured of the optical pulse.

CONSTITUTION: When a distance between an optical pulse generator 1 and a detector 2, and an object to be measured 5, and a velocity of light are denoted as l and C, respectively, the time (t) when an optical pulse emitted from an optical pulse generator L is reflected by an object to be measured 5 and reaches the detector 2, and a detection pulse is generated becomes (t) = 2l/c. When the time required for each operation in the detector 2, a control part 3 and the optical pulse generator 1, namely, a distance measuring meter 4 is denoted as Δt, the number of detection pulses generated from the detector 2 becomes 1/(t + Δt) = c/2l per unit time. In this case, since Δt becomes a specific value in accordance with a device to be used, it can be corrected easily. Accordingly, by measuring the number of detection pulses generated in the measuring time set in advance, a distance to a desired object to be measured 5 can be measured with high accuracy.