An image processing apparatus is provided that can define the change amount of a quantizing parameter by suitably reflecting the complexity of image data in the case, when the quantizing parameter is increased a predetermined unit amount, the coarseness the image data of motion picture is quantized becomes r times. An activity computing circuit generates an activity Nact.sub.j serving as a complexity of the image data. A .DELTA.Q computing circuit defines a corresponding relationship between activity Nact.sub.j and change amount data .DELTA.Q such that the change amount data .DELTA.Q of quantizing parameter increases 1 as the activity Nact.sub.j becomes 1.12 times, to thereby acquire change amount data .DELTA.Q corresponding to the activity Nact.sub.j generated by the activity computing circuit.