Image data scanned by way of a scanner controller is transferred from a memory controller to a memory by way of a G bus. A CPU reduces the image data stored in the memory by thinning processing or the like, and displays the image data on an operation panel by way of a B bus and interface. In this manner, an image can be input using the first bus while data transferred by way of the first bus is output by way of the second bus. This enables processing using image data which is being input, such as processing of immediately displaying an input image.