A position measuring apparatus which measures a position of a position measurement target easily and accurately without using any parameter inside a camera in the measurement, based on images captured from mutually different viewpoints. The position measuring apparatus which measures the three-dimensional position of the position measurement target, based on the input images captured from the mutually different viewpoints, and the position measuring apparatus includes: a ray information storage unit configured to store ray information in which each of ray vectors is associated with a corresponding one of pixels in one of the input images, each of the ray vectors indicating a forward direction of a light incident onto an optical system for a corresponding one of the input images; and a position measuring unit configured to measure the three-dimensional position of the position measurement target, using the ray information stored in the ray information storage unit.