An image forming apparatus and a method of controlling the same are provided. The image forming apparatus includes a document feeder to feed an original document, a time delay integration image sensor to scan the original document and read image data, and a controller to activate a time delay integration function of the time delay integration image sensor when a direction for feed of the original document corresponds to a sub-scanning direction of the time delay integration image sensor, and to deactivate the time delay integration function of the time delay integration image sensor when the direction for feed of the original document does not correspond to the sub-scanning direction of the time delay integration image sensor, during reading of the original document.