To provide a mechanism which facilitates adjusting a ribbon tension in a thermal transfer printer.

The mechanism includes a shaft coupled to an ink ribbon, a knob coupled to the shaft, a clutch plate for generating a torque by friction to the knob, a spring for applying a pressing force to the clutch plate, and a pressing member coupled to the knob for adjusting the pressing force of the spring. A compression amount of the spring is changed over along an inclined grooved cam formed to the pressing member, whereby the pressing force applied to the clutch is adjusted. The torque generated by the clutch mechanism is thus adjusted.