A document type discriminating apparatus is provided in which discrimination as to whether or not a document is a duplicate is made with high degree of accuracy. The document type discriminating apparatus includes means for discriminating whether a type of a screen pattern used in an image captured by reading a document is a line screen, means for detecting whether a value indicating a change in a period of the screen used in the image exceeds a predetermined value, means for detecting whether a value indicating sharpness of an edge seen in the image is lower than a predetermined value, means for detecting whether a value indicating a blur in an edge color seen in the image exceeds a predetermined value, and means for discriminating that the document is a duplicate when at least two out of the four detection results mentioned above are true.