An inkjet printer configured to perform multi-gradation printing, comprising: - at least one inkjet head including nozzles for ejecting ink droplets to form a line of a plurality of dots; - an ejection control section configured to supply, to a nozzle, an ejection control signal corresponding to either one among plural types of ejection control signal corresponding to plural levels of ink dot size; - a dot visual confirmation part configured to pick up an image of ink dots formed on a medium or a line formed by juxtaposed dots, and - an image forming device configured to; calculate a parameter corresponding to ink volume on the basis of the image picked up by the dot visual confirmation part; create or update nozzle information representing an ejection characteristic of an abnormal nozzle in the respective inkjet heads on the basis of the parameter; and form, on the basis of the nozzle information, printable data through which the ink printer executes correction corresponding to the ejection characteristic of the abnormal nozzle, characterized in that: the ejection control section is configured to - change an ejection control signal applied at the time of forming a part among the plurality of dots depending on whether a nozzle is abnormal or normal; and - supply, in case a nozzle forming the line of the plurality of dots is abnormal, that ejection control signal corresponding to the part of the dots, which is different, in ink dot size, from the ejection control signal supplied when the nozzle is normal; and - measure a difference between the volume of ink droplets ejected by a nozzle depending on an ejection control signal and a predetermined standard value, determine whether the nozzle is normal or abnormal depending on whether the difference is within or out of a predetermined permitted range, and change the control of ejection of the ink droplets. - at least one inkjet head including nozzles for ejecting ink droplets to form a line of a plurality of dots; - an ejection control section configured to supply, to a nozzle, an ejection control signal corresponding to either one among plural types of ejection control signal corresponding to plural levels of ink dot size; - a dot visual confirmation part configured to pick up an image of ink dots formed on a medium or a line formed by juxtaposed dots, and - an image forming device configured to; calculate a parameter corresponding to ink volume on the basis of the image picked up by the dot visual confirmation part; create or update nozzle information representing an ejection characteristic of an abnormal nozzle in the respective inkjet heads on the basis of the parameter; and form, on the basis of the nozzle information, printable data through which the ink printer executes correction corresponding to the ejection characteristic of the abnormal nozzle, characterized in that: - change an ejection control signal applied at the time of forming a part among the plurality of dots depending on whether a nozzle is abnormal or normal; and - supply, in case a nozzle forming the line of the plurality of dots is abnormal, that ejection control signal corresponding to the part of the dots, which is different, in ink dot size, from the ejection control signal supplied when the nozzle is normal; and - measure a difference between the volume of ink droplets ejected by a nozzle depending on an ejection control signal and a predetermined standard value, determine whether the nozzle is normal or abnormal depending on whether the difference is within or out of a predetermined permitted range, and change the control of ejection of the ink droplets.