An electrostatic developing toner which can effectively suppress image fogging*1 by setting a ratio (d/D) of the average particle diameter D of the toner and the average particle diameter d of iron oxide particles contained in the toner as a colorant to within a predetermined range, and by setting the value of a ratio (.sigma.r/.sigma.s) between the residual magnetization .sigma.r and saturation magnetization .sigma.s of the iron oxide particles to a predetermined value or less, is provided. The value of the ratio (d/D) of the average particle diameter D of the toner and the average particle diameter d of iron oxide particles contained in the toner as a colorant is set to within the range of 0.01-0.03, and the value of the ratio (.sigma.r/.sigma.s) between the residual magnetization .sigma.r and saturation magnetization .sigma.s of the iron oxide particles is set to 0.3 or less.