1. An image reading system comprising a reading apparatus capable of reading an original and a host computer, said host computer and said reading apparatus being connected to each other through an interface capable of two-way communication, said host computer including: a storage unit having a finite capacity and capable of reading and writing data; a reading setting selection unit capable of selecting a reading setting in said reading apparatus; a setting changing unit for checking a size of an available area in said storage unit when reading is started in said reading apparatus, comparing the size of the available area with a size of image data read by said reading apparatus, and changing the reading setting in said reading setting selection unit if the size of the image data is larger; a change content notification unit for notifying a user of change contents before said setting changing unit changes the reading setting; and a selection unit for choosing between continuing processing and not continuing the processing after a notification is provided from said change content notification unit, wherein said setting changing unit changes the reading setting in accordance with the contents from said change content notification unit if said selection unit chooses to continue the processing, and holds the reading setting without changing the setting if said selection unit does not choose to continue the processing.