PURPOSE: To hole a normal printing operation for a long period by providing polishing means of a type wire between a print head and a platen, and uniformly polishing the end of each wire by the relative movement of the polishing means and the head.

CONSTITUTION: When a carriage 2 is moved to the left end side of a platen 6 and a print head 1 is disposed on a polishing unit 7, a grindstone 20 and an elastic unit 22 are pressed to the platen 6 side by the head 1, and the unit 22 presses the grindstone 20 on the head 1 while deflecting. When the carriage is moved, the grindstone 20 polishes the front guide 19 of the head 1 and the end of the wire 8. The gaps among the wire 8, the ink ribbon 4 and a printing sheet 5 can be always maintained constantly by this polishing to perform normal printing operation.