To provide an impact printer which can prevent a printing defect from being caused by a decrease in the local ink concentration of an ink ribbon.

The local ink concentration of the traveling ink ribbon 11 is measured by a concentration measuring means 40; the traveling-direction length of an ink concentration-decreased part on the ink ribbon 11 is detected by a concentration-decreased-part detecting means 50 according to the measured ink concentration; and the traveling and printing operation of the ink ribbon 11 are controlled by a printing control means 60 so as to avoid the application of the ink concentration-decreased part on the ink ribbon 11 to printing on the basis of the result of detection.