1. An image processing apparatus comprising: input means for inputting a document image; first detecting means for detecting orientation of the document image that has been input by said input means; second detecting means for detecting size of the document image that has been input by said input means; and image processing means for reducing the document image that has been input by said input means, at a magnification according to detection results obtained by said first and second detecting means, and arranging a plurality of document images as a single image.