Provided is an image reader including: a transparent original mounting plate on which an original is mounted; a support which has an appearance larger than that of the original mounting plate and supports the original mounting plate; a reading unit which optically reads the original placed on the original mounting plate; a movement unit which moves the reading unit in a predetermined direction within a readable area; and a reference location specifying plate having a positioning hole and a reference mark hole, wherein the support has a positioning protrusion within the readable area, the reference location specifying plate is positioned and fixed with respect to the support by inserting the positioning protrusion into the positioning hole, and the reading unit optically detects the location of the reference mark hole and specifies a reference location of an original reading area from the detected location of the reference mark hole.