An image reading apparatus according to this invention includes a document conveyance unit mounted movably from a position facing an upper surface of a document table to an upper position for conveying a document medium to place the document medium on the document table, a reading unit having an aperture for optically reading information from the document medium, a shielding member arranged to be slidable in a direction parallel to the upper surface of the document table for shielding the aperture, a detection unit for detecting whether the document conveyance unit covers the upper surface of the document table, and a control unit for controlling movement of the shielding member. With the image forming apparatus having such the structure, a document reading time can be shortened where successively reading document media of plural sheets while preventing foreign materials from attaching to the reading unit.