To provide a marker detection device which can prevent a marker from being erroneously detected.

This marker detection device has optical sensors 1 and 2 which can emit light to an ink ribbon and generate an output complying with a light receiving level by receiving reflected light from the ink ribbon and a control circuit 4 which can detect a marker in accordance with signal levels of output signals from the optical sensors 1 and 2 and a threshold value. The control circuit 4 sets a threshold to a value complying with the signal levels of the output signals obtained from the optical sensors 1 and 2 during detecting a marker of such a type other than a pertinent target type, when the control circuit 4 determines that the marker of the pertinent target type is not detected during detecting the marker and further, it is determined that the marker of the type other than the pertinent target type is detected.