A position information acquisition device for acquiring position information of a position acquisition target arranged in a space includes a processor configured to detect light that is based on identification information included in-common in captured images that are images of the space captured from a plurality of shooting directions that are different from each other, acquire a three-dimensional position in the space of the position information acquisition target identified by the identification information, based on detection positions of the detected light in the captured images, and position information of image capturing devices during capturing performed by the image capturing devices, acquire reliability degree information of the acquired three-dimensional position of the position information acquisition target, based on information relating to an imaging state of each image capturing device during capturing of the captured images, and store the acquired the reliability degree information in a storage.