1. A reading apparatus configured to read a plurality of colorimetric patches in different colors formed on a paper sheet and trigger patches formed so as to correspond to the colorimetric patches, comprising: a colorimeter configured to read the colorimetric patches formed on the paper sheet; a trigger sensor configured to read the trigger patches formed on the paper sheet; and a controller configured to control a reading region at which the colorimeter reads the colorimetric patch on the basis of the trigger patches read by the trigger sensor, wherein the controller has a colorimetry region determination mode in which the reading region at which the colorimeter reads the colorimetric patch is determined on the basis of reading results for the trigger patches and a colorimetry adjustment mode in which the reading region determined in the colorimetry region determination mode is controlled so as to be read by the colorimeter, and in the colorimetry region determination mode, after the reading regions for the colorimetric patches are set to states where the reading regions for the colorimetric patches are gradually shifted in a reading direction with respect to the respective reading results for the trigger patches, the reading results for the colorimetric patches by the colorimeter are collected and thereafter, a region for which a state consistent with a characteristic of the colorimetric patch has been obtained as the reading result is determined as the reading region.