In order to provide an image processing apparatus and an image processing method whereby a high quality output image can be consistently obtained, regardless of the order in which an operator sets the parameters for the performance of filtering, (I) a GUI module (9a) stores, in an input value storage area (9p) of a RAM, reference signs that are employed for first to fourth processes for the filtering of reduced image data, and (II) a filtering module (9f) refers to the reference signs in the input value storage area (9p) when performing the first to the fourth processes for the filtering of input image data, and obtains output image data.