An image reading apparatus includes a main body and a reading unit. The reading unit includes: a document table; a lower supporting member that supports the document table from below; an upper supporting member that contacts an upper side of the document table and clamps the document table with the lower supporting member; and a reading device. The main body includes an exterior member arranged in a position adjacent to the upper supporting member when the reading unit is in a close position. One of the upper supporting member and the exterior member includes an abutting portion and the other includes an abutted portion so as to configure a positioning mechanism for establishing positioning of a relative position between the upper supporting member and the exterior member in an up-down direction.