Patent ID: 7106423

Claim:
A distance measuring device comprising: light emitting means that projects a beam of light onto an object to be measured; light detecting means that detects the light reflected from the object, at a light detecting position corresponding to the distance to the object, and, based on the light detecting position, outputs a long-range side signal that increases in value as the object is positioned farther away from the distance measuring device at a certain intensity of the detected light, and a short-range side signal that increases in value as the object is positioned closer to the distance measuring device at a certain intensity of the detected light; calculation means that calculates a ratio between the short-range side signal and the long-range side signal and outputs an output ratio signal; luminance measuring means that measures luminance of the outside light; threshold setting means that adjusts an infinity determination threshold value such that the infinity determination threshold value is set at a value corresponding to a farther position as lower luminance is measured by said luminance measuring means, and the infinity determination threshold value is set at a value corresponding to a closer position as a higher luminance is measured by said luminance measuring means; and conversion means that compares the output ratio signal with the infinity determination threshold value to determine whether the output ratio signal corresponds to a shorter range side rather than of the infinity determination threshold value, and, if so, converts the output ratio signal into a distance signal using a predetermined conversion formula, and, if not converts the output ratio signal into a predetermined distance signal having a fixed value.