1. An image collating apparatus for sequentially collating the image of a document read by an image reader with a plurality of document images preregistered in a data base and determining the type of said document by detecting the coincidence between the images, comprising: a plurality of image readers having different read sizes connected to an image input unit; a preregistered image read circuit for sequentially reading the document images preregistered in the data base; a document size determination processing circuit for detecting the document ends from the document image input from said image readers and determining the document size; an image retrieval circuit for setting the size of said read document to the size of the preregistered image by retrieving said read preregistered image in accordance with the read document size in the case where the read document size is smaller than said preregistered document size, and by retrieving said read document image from one direction in accordance with the size of said preregistered image in the case where the read document size is larger than the size of said preregistered image; a feature extraction processing circuit for extracting the document feature from the document image set to said preregistered image in size by said image retrieval circuit; a feature collation processing circuit for sequentially matching the extracted document feature with the feature of the preregistered image set to said document image in size by said image retrieval circuit; and a document determination circuit for determining the type of the document based on said preregistered image in the case where the document feature coincides with the feature of the preregistered image.