An image-reading apparatus, including a housing, a document table placed on the housing for receiving document, a movable optical unit placed on the document table for reading the image information on the document, the movable optical unit being placed reciprocally movably in the housing in directions parallel to the document table; a locking member placed movably on the housing external face for locking the movable optical unit; and a holding mechanism for holding the locking member variable in posture between a first posture of locking the movable optical unit and a second posture of unlocking the movable optical unit.