a cassette comprises a driving roller provided with a device for preventing the reverse rotation , a driving pulley connected with the driving roller , a rubber belt for transmitting a motion of the driving pulley and a take - up spool on which a film ribbon is wound , and optionally a mechanism for maintaining tension occurred in the film ribbon constant . this arrangement ensures a unidirectional rotation of the driving roller and a correct tension of the ribbon at all times , whereby high quality in printing can be attained .