A medium winder, includes: a winding roller that winds a medium discharged from an image formation apparatus into a roll shape; first and second rollers that guide the medium to the winding roller; a dancer roller provided between the first and second rollers in the medium conveyance direction and movable upwardly and downwardly while contacting from above the medium between the first and second rollers; a winding driver that rotates the winding roller; a detector that detects the dancer roller; a dancer roller position recognition portion that recognizes the position of the dancer roller based on a detection result by the detector; and a winding drive controller that controls the winding driver. In an operation of unwinding the medium, the winding drive controller moves the dancer roller up and down by reducing or increasing the unwinding velocity of the medium based on a position of the dancer roller.