Abstract: In forming an image by developing an electrostatic latent image with a grey toner, a mixture of a white toner and a black toner is used as the grey toner and the ratio (D) of the black toner to the entire toner, the developing voltage (DV) and the image density (ID) are set so that the requirement represented by the following formula is satisfied:ID=A.sub.2 .times.(1-e.sup.-K 2.sup.D).times.(1-e.sup.-K 3.sup.DV)wherein A.sub.2 is a number of from 0.5 to 2.5, K.sub.2 is a number of from 1 to 2, and K.sub.3 is a number of from 0.001 to 0.01.According to this process, a copy having a grey image area corresponding precisely to the image of an original is obtained.