A sheet de-curling device: including a first de-curling roller, structured of a round axial shaft and a long bar-shaped member, wherein the long bar-shaped member is spiraled on the round axial shaft clockwise from a predetermined portion of a center of the round axial shaft toward a left end of the round axial shaft, and counterclockwise from the predetermined portion of the center of the round axial shaft toward a right end of the round axial shaft with the same spiraling pitch; a second de-curling roller, structured of a round axial shaft and a long bar-shaped member, wherein the long bar-shaped member is spiraled on the round axial shaft in opposite spiraling directions against the first de-curling roller; and a driving mechanism which rotates the paired first and second de-curling rollers.