1. A thermal transfer printer comprising: a thermal head including a plurality of heating elements and causing the heating elements to generate heat and transfer ink onto a sheet to print an image on the sheet; a storage unit for storing a first correspondence between a heating element in the thermal head and a correction amount of energy applied to the heating element, and a second correspondence between a tone value of an image to be printed and an adjustment coefficient of the correction amount, the first correspondence being generated from a density distribution of a test image printed based on image data of a single tone, wherein the adjustment coefficient is reduced as a printing density indicated by the tone value is higher; and a control unit for correcting energy applied to each of the heating elements by an amount obtained by multiplying the correction amount for the heating element obtained from the first correspondence by the adjustment coefficient obtained from the second correspondence according to a tone value of an image to be newly printed.