A moisture data-acquiring device has a force-applying unit for applying an external force to a sheet, a force-receiving unit for receiving the external force through the sheet, a signal outputting unit for outputting a signal reflecting a mechanical property of the sheet which unit is placed on at least one of the force-applying unit and the force-receiving unit, and a moisture data-acquiring unit for acquiring data on moisture of the sheet based on the signal from the signal outputting unit.