1. An apparatus for distance measurement, in which a depth distance down to a target point is measured as a phase is entered to said apparatus as an input, said phase being a quantity representing a change of a pattern projected on a target point whose depth distance is to be measured; said pattern being varied depending on directions of projection from pattern projection unit; said phase being measured by observing a reflection of said pattern; said apparatus comprising: a phase cross ratio calculating unit for receiving a phase of said target point and phases of three reference points lying on a line of light on which said target point has been measured, and for calculating a phase cross ratio to output the phase cross ratio calculated; and a depth distance calculating unit for receiving the depth distances of said reference points and said phase cross ratio and calculating the depth distance of said target point by exploiting the equality of said phase cross ratio and a depth distance cross ratio of depth distances among said reference points and said target point.