An apparatus for determining the density unevenness of an ink jet head includes a characteristic data generation unit which calculates characteristic values about ink amounts ejected from all nozzles of the ink jet head, respectively. A decision parameter acquisition unit arranges the characteristic values in the order the nozzles are arranged and calculates a decision parameter from changes in the characteristic values about those of the nozzles, which exist in a predetermined section. A decision unit compares the decision parameter with a predetermined threshold value, thereby determining the density unevenness of the ink jet head.