The image scanning apparatus capable of reading an image by scanning a carriage equipped with a light source, mirrors and the like in a sub-scanning direction of an original document O, is provided, and in this apparatus, the stepping motor is used to drive the carriage, and an open loop control and switching of the exciter are carried out. With this structure, the scanning speed of the carriage can be increased to be higher than the set speed once, and then reduced to the set speed, thus making it possible to shorten the time for the carriage to move from the home position to the top of the document to be scanned, while suppressing the load on the CPU.