1. A method of judging the truth of a paper type, comprising the steps of: performing first truth judgment processing with respect to a paper type to be examined; performing second truth judgment processing with respect to the paper type to be examined only when it is judged that the paper type to be examined is not a false paper type in the first truth judgment processing; and judging that the paper type to be examined is a true paper type only when it is judged that the paper type to be examined is not a false paper type in the second truth judgment processing, the first truth judgment processing comprising a first step of extracting, on the basis of characteristic amounts of the paper type to be examined which are read from a plurality of portions on the paper type and reference data previously found with respect to the plurality of portions, random components for each of the characteristic amounts of the paper type, a second step of presuming, on the basis of the extracted random components for each of the characteristic amounts and a predetermined forecast model of dirt components, the dirt components for the plurality of portions on the paper type to be examined, and a third step of judging the truth of the paper type to be examined on the basis of the presumed dirt components and the extracted random components, the second truth judgment processing comprising a fourth step of previously selecting from the characteristic amounts of the paper type to be examined which are read from the plurality of portions on the paper type and second reference data previously found with respect to the plurality of portions the characteristic amounts and the second reference data with respect to a plurality of positions where an operation is to be executed as ones suitable for judgment and calculating the goodness of fit of the characteristic amount and the second reference data, and a fifth step of judging the truth of the paper type to be examined on the basis of the calculated goodness of fit.