An image reading apparatus includes a document table that is transparent, a read unit that reads a document placed on the document table through the document table so as to generate image data representing a read image of the document, an extraction unit that converts the image data of the read result of the read unit into edge image data representing an edge image and extracts edge points satisfying a predetermined condition as edge points corresponding to a side of the document placed on the document table from the edge image data, an outer margin recognition unit that approximates the edge points corresponding to each side of the document extracted by the extraction unit to a line so as to recognize an outer margin of the document, and a likelihood evaluation unit that evaluates the likelihood of the outer margin recognized by the outer margin recognition unit.