Even if a user sets an erroneous setting to a sheet, in order to provide an image formation system which can recycle sheets and improve operability without executing incorrect processing to the sheet, a reference value, which is referred in confirming an abnormal state of the sheet to be conveyed, before a generation of sheet size information is made to differ from the reference value after the generation of the sheet size information on the basis of a sheet detected result. In accordance with the sheet size information to be confirmed and the sheet size information acquired according to an instruction from an operator, processing corresponding to the instruction from the operator to the sheet is invalidated. An image formation operation is interrupted in accordance with the sheet size information to be confirmed and the sheet size information acquired according to the instruction from the operator.