An MFP includes a scanner to read an image, and a printer to form the image on a sheet, in which the scanner includes a document table on which a document as an image reading object is placed, a platen cover that holds the document to the document table, a carriage that moves along the document table, a document size detecting element that detects a size of the document at a position in front of an image reading start position of the document in an image reading direction, and a control device that detects the document size based on an output of the document size detecting element. According to the MFP, it is possible to realize shortening of an image reading time while reduction in thickness of the apparatus and reduction in cost are kept.