In a rangefinder, if sensor data initially received by a sensor data storage part from an A/D converter includes data with low contrast, the sensor data storage part receives the sensor data at least one additional time, adds additionally received sensor data to the initially received sensor data, and stores their sum. In accordance with the sum of sensor data stored in the sensor data storage part, a correlation calculation and a rangefinding calculation are carried out, which enables rangefinding with respect to an object having low contrast. Also, the time required for A/D-converting the sensor data again and adding the resulting data to those initially obtained is much shorter than the integration time required for integrating output signals of a pair of line sensors a second time for a region with low luminance and low contrast.