1. A rangefinder apparatus of a passive rangefinding type for successively carrying out a correlation calculation for each of a plurality of rangefinding areas according to respective output signals of a pair of light-detecting sensors on which a pair of images are formed by external light from an object to be subjected to rangefinding, and calculating distance to the object according to a minimum value exhibiting highest degree of correlation in correlation values obtained by correlation calculations of individual rangefinding areas, the rangefinder apparatus comprising: effective minimum value certifying means for comparing a minimum value, exhibiting the smallest value of correlation values calculated for each rangefinding area, with a reference value for degree of correlation and certifying a minimum value smaller than the reference value as an effective minimum value, effective for a rangefinding calculation; distance calculating means for calculating the distance to the object according to the effective value certified for each rangefinding area; and correlation calculation restricting means for omitting the correlation calculation within a specific distance range, farther by at least a predetermined amount than the shortest distance calculated according to the effective minimum value in the correlation calculation, for a rangefinding area to be later subjected to the correlation calculation, when the effective minimum value exists in the rangefinding area earlier subjected to the correlation calculations, wherein the effective minimum value certifying means is configured such that the reference value for the degree of correlation is set according to contrast of an image of the object and attains a high value when the contrast is high and becomes lower as the contrast becomes lower.