To provide a thermal transfer printer in which good printing can be always obtained by holding a ribbon tension when a finely regulated value of a drive voltage of a first motor is input even if a ribbon diameter of a winding side is changed.

A winding force is generated at a thermal transfer ribbon by the first motor 49, and a back tension force is generated at the ribbon by a second motor 47. A first drive voltage is calculated in response to the ribbon diameter so that a tension force suitable for the ribbon diameter when the finely regulated value of the drive voltage of the first motor 49 is input is maintained constant for the finely regulated value of the input drive voltage of the first motor 49, and stored. A motor drive control means controls the first motor 49 by the first drive voltage finely regulated after the finely regulated value is input.