An image reading apparatus is attached to the top of a PDA. During the image reading operation, an operation state control signal is output from the image reading apparatus to the PDA. According to the signal, the intensity of an input display unit not required during the operation can be reduced. Additionally, the power supply or the supply of a signal not required during the operation is stopped. Furthermore, an LED of the PDA issues a notification of an operation state by lighting, blinking, or turning-off. When the input display unit displays an image, an erect image and an inverted image are appropriately switched depending on the operation state. During an image reading operation, input by input buttons and a touch panel of the input display unit are nullified to avoid the occurrence of a malfunction.