In a magnet brush type image developing method of the present invention, at least one position where brush chains formed by magnetic carrier grains rise exists in a portion where an electric field formed between a facing zone where an image carrier and a developer carrier face each other has a strength E(V/m) expressed as:

##EQU1##

• where B is representative of T_cD³_c/(100-T_c)d³_T, A denotes a mean amount of charge (C/kg) deposited on the toner grains T_cdenotes the content of toner grains (wt %), d denotes the mean grain size (m) of the toner grains, D denotes the mean grain size (m) of the magnetic carrier grains, _T denotes the specific weight (kg/m³) of the toner grains, _c denotes the specific gravity (kg/m³) of the carrier grains, _o is 8.85410^-12 (F/m), R denotes the diameter of the developer carrier, and V_SL denotes the linear velocity of the developer carrier.