Original reading apparatus

An original reading apparatus, comprising:

• a platen including a surface on which an original is to be placed;
• an illumination unit configured to illuminate the original placed on the platen while moving in a first direction;
• a reading element configured to read an image of the original placed on the platen by receiving light which is reflected by the original illuminated by the illumination unit;
• a sensor provided below the platen and configured to detect presence or absence of the original on the platen to identify a size of the original;
• and
• a holding member configured to hold the sensor, the holding member being movable between a first position for the sensor identifying a first size standard and a second position for the sensor identifying a second size standard in the first direction, the holding member including an operating portion used by an operator to move the holding member in the first direction, wherein the holding member extends from a first space to a second space through an opening provided on a wall, the wall intersecting a second direction which is orthogonal to the first direction and is parallel to the surface of the platen, the wall provided between the first space and the second space in the second direction, the sensor, the illumination unit, and the reading element being located in the first space, the operating portion being located in the second space.