Abstract: Reflected light of each beam projected toward an object to be measured is received to provide a far signal and a near signal, and the far signal is compared with a preset clamp signal. The larger signal resulting from the comparison is outputted from a clamping circuit and a ratio of the output signal and the near signal is calculated to obtain an output ratio signal. Output ratio signals against light emissions from a light projecting unit are accumulated in an integral operation to obtain an integral signal. The integral signal is transformed to a distance signal according to the distance by either of different transformation equations, based on whether the number of clamp signals outputted as output signals from the clamping circuit during the integral operation is not less than a set number.