An image forming apparatus including an image bearer, a magnetic field generator, a two-component developer bearer, a developing electric field generator, and an image developer. The two-component developer has at least a current speed index (25FRI) of from 0 to 2.0, which is determined by the following formula: 25FRI=(total energy at 10 mm/s/total energy at 100 mm/s). The total energy is an integral sum of a rotary torque and a vertical load when a blade of a powder fluidity analyzer spirally rotates at 10 mm/s and 100 mm/s, respectively, in the developer having a volume of 25 ml after idly agitated in the image developer for 10 minutes.