PURPOSE: To preserve the fine line and to suppress the picture quality of the other part at the time of the variable power processing concerning an image variable power processor to perform the variable power processing for the binarized input image.

CONSTITUTION: The processor is constituted of a fine line deciding means 1 to decide whether or not the remark picture element of the input binary image data is a part of the fine line, a first variable power means 2 to perform the variable power processing so that the fine line cannot be eliminated for the input binary image data, second variable power means 3 and 4 to convert the input binary image data into the multi-valued image data and convert them into the binary image data again after the variable power processing is performed, and a selecting means 5 to select respectively the image data variable-power-performed by the first variable power means 2 when the fine line is detected by the fine line deciding means 1 and the image data variable-power-performed by the second variable power means 3 and 4 when the non-fine line is detected by the fine line deciding means 1. The first variable power means 2 is the means with the logical OR method, and the second variable power means 3 and 4, after the density after varying the power is calculated by the projection method or the interpolation method, perform the interpolation by the quantizing error accompanying the binarization of the peripheral picture element binarized already and perform the binarization.