1. An installation error estimating apparatus that estimates installation error of a tag reader that positions a wireless tag, the installation error estimating apparatus comprising: a predicted pattern acquisition section that acquires a predicted positioning distribution pattern, which is obtained by calculating a characteristic pattern of a predicted positioning distribution obtained by predicting a positioning distribution, for each observation point where the wireless tag is installed and positioned; an observation data input section to which a positioning result of the tag reader with respect to the wireless tag is input as observation data; a variance pattern analysis section that calculates as a measured positioning distribution pattern a characteristic pattern of a measured positioning distribution, which is obtained by means of statistical analysis of a positioning result, for each observation point, based on observation data input by means of the observation data input section; and an installation error estimating section that calculates installation error of the tag reader using a predicted positioning distribution pattern acquired by the predicted pattern acquisition section and a measured positioning distribution pattern calculated by the variance pattern analysis section.