There is provided an image reading apparatus and a control method therefor, which can suppress the influence of external light, and obtain an appropriate read image. To accomplish this, the image reading apparatus executes a Light-on reading processing for turning on an LED and causing a sensor to read an original document on a original platen at the first resolution, and a Light-off reading processing for turning off a light source and causing the sensor to read the original document on the original platen at the second resolution. In accordance with the influence of external light in an Light-off mode image read by the Light-off reading processing, the image reading apparatus removes the influence of external light in a Light-on mode image read by the Light-on reading processing.