Patent ID: 7903235

Claim:
A surveying instrument comprising: a light receiving section for receiving a reference pulse light and a measurement pulse light as a received light signal; an extract signal forming means for forming an extract signal that is a part of a frequency component extracted from the received light signal; an amplifier for amplifying a minute level signal in the extract signal with a high amplification rate, the minute level signal being in a proximity of a zero cross point; a timing signal forming section for forming a timing signal from the received light signal, by using an amplified signal of the minute level signal amplified by the amplifier; and a measurement value calculating section for calculating a delay time of the measurement pulse light in relation to the reference pulse light or a distance from a measuring object based on a light receiving time difference between a timing signal formed from the reference pulse light and a timing signal formed from the measurement pulse light, wherein said amplifier includes one of a limiting amplifier or a log amplifier with a higher amplification rate of the minute level signal than an amplification rate of a signal in the extract signal of areas other than the proximity of the zero cross point.