The present invention provides a composite color image forming method. The method includes electrically charging a latent image-holding member; exposing the charged latent image-holding member to light to form an electrostatic latent image; developing the electrostatic latent image with a two-component developer containing toner particles of one color and a carrier to form a toner image on the latent image-holding member; primarily transferring the toner image from the latent image-holding member to an intermediate transfer member; repeating the electrically charging, the exposing, the developing, and the primarily transferring, while the toner particles are replaced with toner particles of different color, to form a composite color image on the intermediate transfer member; and secondarily transferring the composite color image from the intermediate transfer member to a recording medium. The carrier contains magnetic substance-dispersed core particles in which a magnetic substance is dispersed in a resin, and a coating layer that coats the surface of each of the magnetic substance-dispersed core particles at a covering rate of 95% or more. In addition, the carrier has a degree of circularity of 0.970 or more. The intermediate transfer member is a belt that has a substrate whose Young's modulus is in the range of 3,000 to 6,500 MPa. During the primary transferring, primary transfer nip pressure is in the range of 8 to 20 gf/cm, and a value (T/P) obtained by dividing a primary transfer current value T (μA) by a processing speed P (mm/sec) is from 0.08 to 0.18.