A distance measuring device for an automatic focusing camera includes a light receiving lens and a multilayer printed circuit board mounted on a holder. A potting frame is provided on the lens-facing side surface of the printed circuit board. An optical sensor and an IC are both mounted within a space enclosed by the potting frame and simultaneously sealed by a protecting resin. Resistors and capacitors of a distance measuring circuit are mounted on the opposite surface of the printed circuit board. The two surfaces of the printed circuit board are connected to each other via a through hole to construct the distance measuring circuit. The protecting resin transmits light having specified wavelengths. The light reflected from a subject to be photographed is received by the optical sensor after passing through the protecting resin, and the distance to the subject is calculated on the basis of the received light data.