In an image processing apparatus capable of enlarging/reducing operation according to the invention, there are provided an input buffer for storing an image data, an enlargement/reduction circuit for performing the enlargement/reduction processing of the image data outputted from the input buffer, an output buffer for storing the enlarged/reduced image data, and a timing circuit for controlling processing timing for the image data through the input buffer, the enlargement/reduction circuit and the output buffer. The timing circuit respectively controls the data read-out timing from the input buffer and the data write-in timing into the output buffer in accordance with the designated enlargement/reduction ratio by regulating the frequency of clock pulse.