PURPOSE: To detect the existence of a medium while simultaneously distinguish the type thereof in a thermal transferring recording device by making media reflect the radiating light from a light emitting element and receiving the reflected lights each having different reflecting angle by a plurality of light receiving elements.

CONSTITUTION: A medium detecting device 2 has a light emitting element 3 for radiating a radiating light L1 with an incident angle θ1 to a medium 1, a light receiving element 4 for receiving a reflected light L2 with a reflecting angle θ2 (θ2=θ1), and a light receiving element 5 for receiving a reflected light L3 with a reflecting angle θ3 (θ3>θ1). When a medium of high irregular reflection, e.g., an ordinary sheet of paper 1a comes in, since the spreading angle 1 of irregular reflection is approx. 80°, the intensities of irregular reflections L2, L3 which both light receiving elements 4, 3 receive are higher than a defined level causing each detected signal to be H. On the other hand, when an OHP sheet 1b of low irregular reflection comes in, the spreading angle 2 of irregular reflection is approx. 20°, causing only the light receiving element 4 to output H while leaving the output of the light receiving element 5 at L. Thereby, the type of a medium can be also detected enabling the quality of printing to be kept constant.