PURPOSE: To obtain a mountable ribbon cassette which can be easily molded at low cost by forming a protrusion which extends in an opposite direction at the bottom of each outer plate, at the same time, forming a pair of protrusions which jut out downward in a vertically opposite direction to each of the other protrusions through a gap, on a cassette cover.

CONSTITUTION: A cassette case 12, storing a ribbon 4, a feed roller 5 and a pinch roller 6, is equipped with a guide part for feed-out 171 consisting of an inner plate 141, an outer plate 151 and a bottom plate 161, and a guide part for feed-in 172 consisting of an inner plate 142, an outer plate 152 and a bottom plate 162 in an opposite direction to the guide part 171, formed in a single piece. Protruding parts 181, 182 which jut out in a mutually opposite direction are formed at the bottom of the tip of each outer plate 151, 152. That is, the top of the tip each outer plate 151, 152 is notched. A pair of protrusions 201, 202 are formed in an opposite direction to each protrusion 181, 182 vertically through a gap, projecting downward, on a cassette cover 13.