A curl straightening method applied upon printing on a spread medium in a printing step, the method being provided with a first spreading step of spreading the medium fed out from a medium roll between a feeding step of feeding the medium from the medium roll in which the medium made of a textile fabric and having a predetermined width is wound on a roll core, and the printing step of printing on the medium fed out from the medium roll, and in the first spreading step, spreading of the medium is performed in a state where the medium fed out from the medium roll is stretched on an outer circumference of a first spreader roller rotating about a pivotal axis parallel to a pivotal axis of the medium roll, and the medium has its surface side with a curl stretched on the outer circumference of the first spreader roller.