An inpact dot printer has a ribbon cassette the casing of which is made of plastic. A leaf spring is mounted in the casing so as to be resilient contact with the inked ribbon in the cassette. An element protrudes from the spring to the outside of the casing, and is located at a position where it is in resilient contact with either a carriage of conductive material or a metal part secured to the carriage when the ribbon cassette is installed in position on the carriage. When the printer effects printing operation, static electricity generated on the ribbon is carried away to ground via the protruding element and other components.