An image reading apparatus for reading a document placed on a document positioning plate using a reading sensor unit mounted on a carriage includes a rack member provided in an apparatus body and having rack teeth provided along the moving direction of the carriage, a pinion gear rotatably disposed on the carriage and meshed with the rack teeth, a motor mounted on the carriage and driving the pinion gear, an urging member disposed between the carriage and the reading sensor unit and urging the reading sensor unit toward the document positioning plate, a guide rail provided in the apparatus body and guiding movement of the carriage, and a guide portion provided on the carriage and engaged with the guide rail, wherein the guide portion is pressed toward the guide rail by receiving a reaction force of the urging member at the carriage.