Roller leveler and plate flattening method using the same

A roller leveler for flattening a plate by passing the plate through a pass line, the roller leveler comprising:

• a leveling roll unit including a plurality of leveling rolls arranged on upper and lower sides of the pass line in a staggered manner and configured to rotate so as to pass the plate while flattening the plate sandwiched therebetween;
• a pushing cylinder provided at each of an entrance side and a discharge side of the leveling roll unit, at which the plate enters and is discharged, respectively, and configured to press the plate via the leveling rolls;
• and
• a driving mechanism configured to rotate the leveling rolls to pass the plate,
• wherein
• at least one of the plurality of leveling rolls has a stepped structure, the at least one of the plurality of leveling rolls including a lateral center portion with a large diameter, corresponding to a center portion of the plate with respect to a plate width direction, and a lateral end portion with a small diameter, corresponding to an edge portion of the plate with respect to the plate width direction.