An image forming apparatus includes: a developer carrying member (sleeve) including a magnet and grooves; and an image bearing member (drum). The electrostatic image on the drum is developed with a developer. When a linear speed of the sleeve is Vs, a linear speed of the drum is Vd, a peripheral speed ratio of the sleeve to the drum is α=Vs/Vd, a radius of the sleeve is Rs, a radius of the drum is Rd, a distance of a rectilinear line connecting a most upstream point and a most downstream point in the developing region with respect to the circumferential direction is Lnip, a pitch of the grooves of the sleeve is p, and an arbitrary natural number is n, the following relationship is satisfied: (1−0.05)×np≦2[α×Rd×arcsin(Lnip/2Rd)−Rs×arcsin(Lnip/2Rs)]≦(1+0.05)×np.