An image reading apparatus includes a document table, a read unit that reads a document so as to generate image data representing a read image of the document, a partial prescanning unit, which conveys the read unit in a partial area of a readable area of the document table, and which controls the read unit to execute read operation in the partial area, a corner estimation unit, which converts the image data of the read result of the read unit into edge image data representing an edge image, and which estimates position coordinates on the document table corresponding to two of four corners of the document on the assumption that the placed document is quadrangular based on the edge image data, and a document estimation unit that estimates the state of the placed document based on the estimation result of the corner estimation unit.