PURPOSE:To evade an error in distance measurement due to parallax, an increase in the scale of a two-image relative position detection type distance measuring device, and complexity in adjustment by using one distance measuring optical system in common to a photographic optical system. CONSTITUTION:A photographic lens 1 is used in common as a reference visual- field lens for distance measurement, and a reference visual-field image is formed on a reference visual-field sensor 7. A reference visual-field signal and a comparison visual-field signal obtained from said image and a comparison visual- field image formed on a comparison visual-field sensor 10 through a comparison visual-field lens 8 are made into binary-coded image signal sequences by binary- coding circuits 12 and 13. Both those signal sequences are stored and then while they are shifted relatively and successively, whether the image is in focus or out of focus is detected, bit by bit; and the extent of the shifting performed until a maximum number of focusing is obtained is compared with information on the outward movement position of the photographic lens 1, thus discriminating an in-focus state.
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