This invention is directed to image reading capable of suppressing EMI unwanted radiation while maintaining image quality. To accomplish this, the following processing is executed when reading an original image by a photoelectric transducer. More specifically, a first driving signal where SSCG spread modulation is applied, and a second driving signal where no SSCG spread modulation is applied are generated from a reference signal. Either the first or second driving signal is selected, and a timing signal for reading the original image is generated based on the selected driving signal. The image signal obtained by the photoelectric transducer is latched using the timing signal. The latched image signal is transferred for subsequent image processing. Upon reading a one-line image original, the second driving signal is selected till the completion of the latch operation, and after the latch operation, the first driving signal is selected for an image signal transfer operation.