1. An apparatus for optimizing a non-ejection correction parameter of an ink-jet head, comprising: a test chart data generating device which generates test chart data based on the non-ejection correction parameter for each of a plurality of nozzles provided on the ink-jet head; a read data acquiring device which acquires read data of a test chart recorded on a recording medium by ejecting ink from the plurality of nozzles based on the test chart data while relatively moving the ink-jet head and the recording medium; an evaluating device which evaluates a correction intensity of the non-ejection correction parameter for each of the nozzles based on the acquired read data; a parameter updating device which updates the non-ejection correction parameter for each of the nozzles based on a single variable root-finding algorithm using iteration method from the evaluated correction intensity; a controlling device which optimizes the non-ejection correction parameter for each of the nozzles by repeatedly executing the operations of the test chart data generating device, the read data acquiring device, the evaluating device, and the parameter updating device; and an outputting device which outputs the optimized non-ejection correction parameter for each of the nozzles.