A sheet conveyance control method in an apparatus including a first conveying path for leading a sheet from a feeing port to a discharge port, a second sheet conveying path for leading the sheet to another conveyance destination, and a decoloring processing section configured to decolor an image formed on the sheet includes: detecting the length of the sheet further on a downstream side than the feeding port and further on an upstream side than a branching point of the first and second sheet conveying paths in a sheet conveying direction of the first sheet conveying path; and changing, if the trailing end of the sheet is not detected in a period after the leading end of the sheet is detected and before the leading end of the sheet reaches the branching point, a first flapper to a state in which the sheet is conveyed to the discharge port.