PURPOSE: To provide the binarizing processing method applying binarizing processing to an original picture with higher definition without deterioration in the picture due to the effect of noise or the like onto the original picture.

CONSTITUTION: In the binarizing processing method reading sequentially density data Im,n for each of consecutive picture elements forming a picture and applying the error diffusion method to the read density data to obtain binarized picture data Bm,n from the picture, a threshold level for binarization discrimination 6 with respect to density data of a noticed picture element obtained by being subjected to error diffusion processing 2 is changed based on data 9 obtained by applying smoothing 8 to the density data of the read noticed picture element.