To provide an ink ribbon unit that can prevent a color ink surface of an ink ribbon from being exposed when the ink ribbon is replaced before reeling is completed.

A thermal printer includes: an ink ribbon 3 on which a color ink surface 32 and a non-color ink surface 33 are alternately formed in a conveyance direction, a supply bobbin 4 on which the ink ribbon 3 is wound, a take-up bobbin 5 on which the ink ribbon 3 is to be wound, and a housing 6 that contains the supply bobbin 4 and the take-up bobbin 5. When an error occurs during transferring of an ink on the color ink surface 32, a portion of the ink ribbon exposed from the ink cassette between the supply bobbin 4 and the take-up bobbin 5 is the non-color ink surface 33.