To provide a surveying instrument for measuring difference in required time of light or distance to an object to be measured while covering a wide dynamic range without adjusting light amount. A light pulse emanating from a light emitting section 1 is divided into a reference light cast to a reference light path F1 and a measurement light cast to a measurement light path F2 through which the measurement light travels to and is reflected back from the object to be measured. These two light beams are received with a light receiving section 9. With a multiplex reflection optical fiber Mp1 interposed in the middle of the measurement light path F2, the measurement light comes out as a row of multiplex light pulses attenuating successively in light amount at a constant rate. From this row of pulses, a measurement light of approximately the same in received light level as the reference light may be selected. Based on the selected measurement light and the reference light, the difference between the time required for the measurement light traveling through the measurement light path F2 and the time required for the reference light traveling through the reference light path F1, or the distance to the object to be measured, is measured.