To provide an ink jet printer capable of improving operability for setting a recording medium as compared with a conventional technique.

A medium transport device 40 of an ink jet printer includes: a roller supporting groove 41c rotatably supporting a winding roller 44 winding a recording medium 92; a platen 45 arranged to be opposed to a recording head when the recording head prints an image on the recording medium 92; an upstream roller 46 that is a driven roller rotating to follow movement of the recording medium 92, a rotational amount of which is detected by a rotary encoder 56; a tension application member 48 applying a tension to the recording medium 92; and moving-amount control means for controlling a moving amount of the recording medium 92 on the platen 45 by controlling rotation of the winding roller 44 on the basis of the rotation amount of the upstream roller 46 detected by the rotary encoder 56.