A vehicle-mounted stereo camera device that achieves high-precision distance detection is provided. The provided vehicle-mounted stereo camera device includes a left camera and right camera disposed on a vehicle via a holder to cause visual fields to overlap each other, a stereo processor that calculates a distance to a body outside the vehicle based on images captured by the left camera and right camera and on positions on the vehicle, first and second geomagnetic sensors respectively disposed near the left camera and right camera, and a third geomagnetic sensor disposed on the holder. The stereo processor compares a geomagnetic value detected by the first or second geomagnetic sensor with a geomagnetic value detected by the third geomagnetic sensor, detects a displacement amount of the left camera or right camera, and changes a cutout position in the image captured by the left camera or right camera based on the displacement amount.