1. An image filing apparatus comprising: image reading means for reading an image; a plurality of image data compressing and extending units, each of said plurality of image data compressing and extending units respectively corresponding to one of a plurality of image outputting units and being adapted to compress and extend image data read by said image reading means by a data compressing and extending method different from each other; and control means for selecting an image data compressing and extending unit from said plurality of image data compressing and extending units with respect to one of said plurality of image outputting units in accordance with an output form of said one of said plurality of image outputting units, and outputting the image data extended by the selected image data compressing and extending unit to said one of said plurality of image outputting units, wherein said apparatus further comprises images processing means for changing the scale of the image read by the image reading means in accordance with the number of dots in an image displaying unit, the image processing means changing the scale of the image before compression of the image data.