An image reading apparatus applicable to, for example, an electronic copier or a facsimile transceiver for reading an image by use of CCDs or similar reading elements. A circuit included in the apparatus and not having a time constant is driven at the same time as the start of an image reading operation, while a circuit having a time constant is driven earlier by taking account of the time constant. The apparatus, therefore, reduces electromagnetic interference and saves power while eliminating defective image signals.