To solve the problem that a processing speed is deteriorated due to the huge increase of the storage capacity of large amounts of picture data to be handled by a computer or the necessity of any processing to be executed to the picture data whose data amounts are large.

Processing for reducing data amounts such as thinning processing is executed before original picture data are stored in a spool file 25c1 so that the capacity of the spool file 25c1 can be reduced. Moreover, when a printer 27 is set corresponding to monochrome, and the original picture data are color picture data, the color picture data of each pixel of the original picture data are degraded so that the data amounts of the original picture data can be reduced.