The purpose of obtaining a high resolution image with fewer number of image sensings in an image input device which allocates a planar object such as a document or the like into a plurality of areas for image sensing, and combines the obtained image data for output to a printer or display device or the like.An image reading device using an area sensor as an image sensing element 30 which is stationary in an image sensing unit 14 facing the center of a document 1 on a table 11, and a taking lens 31 moves parallel to the document 1 and the image sensing element 30 to read the images of allocated sections A˜I of the document 1.