The present invention provides a half-tone image processing method utilizing an error diffusion technique which allows for the density adjustment of a half-tone image to be reproduced. When the density of an object pixel is converted into binary-coded data, a binary-coding object value is first calculated by adding a density value of the object pixel to an error sum of binary-coding errors distributed to the object pixel from peripheral pixels around the object pixel. Then, the binary-coding object value is compared with a threshold value TH for judging whether the object pixel is a black pixel or a white pixel. The binary-coding object value is also compared with a reference value GSLVB or GSLVW which can be variably set for the calculation of a binary-coding error HG of the object pixel. The level of the binary-coding error HG can be adjusted by variably setting the reference values GSLVB and GSLVW. Thus, the density adjustment of a half-tone image can be realized.