1. A position measuring apparatus comprising: a first irradiation part that irradiates a first beam to multiple joint object including multiple blocks and multiple joints connecting the multiple blocks; a second irradiation part that irradiates a second beam to the multiple joint object; a capture part that captures images of the multiple joint object; a process part that generates a first difference image and a second difference image by processing the images captured by the capture part, the first difference image being generated according to a difference between an image captured when the first beam is irradiated and an image captured when no beam is irradiated, the second difference image being generated according to a difference between an image captured when the second beam is irradiated and an image captured when no beam is irradiated; an extract part that extracts a contour and a feature point of the multiple joint object from the first difference image; a calculation part that calculates three-dimensional coordinates of a reflection point located on the multiple joint object based on the second difference image; and a determination part that determines position parameters of the multiple joint object by matching the contour, the feature point, and the three-dimensional coordinates with respect to predetermined modeled data of the multiple joint object; wherein the determination part is configured to determine the position parameters of the multiple joint object by calculating position parameters of a center block of the multiple blocks included in the multiple joint object, calculating position parameters of blocks connected to the center block of the multiple joint object, and when uncalculated blocks are connected to blocks whose position parameters are already calculated, obtaining the position parameters of the uncalculated blocks based on the calculated blocks.