A range finding device includes: a light projecting unit having an irradiation domain extending in a horizontal direction, and configured to project intensity-modulated irradiation light; an image capturing unit configured to capture an image of an object irradiated with the irradiation light; a light projection controller configured to control an intensity of the irradiation light in accordance with a timing at which the image capturing unit captures the image; a synchronous detection unit configured to extract a synchronous detection region, in which brightness changes in synchronism with intensity modulation of the irradiation light, from the image captured by the image capturing unit; an edge detector configured to detect an edge of the synchronous detection region; and a range calculator configured to calculate a distance to the object on the basis of the edge of the synchronous detection region detected by the edge detector.